Fallout: New Vegas Reputation

Overview
Reputation in Fallout: New Vegas is a measurement of how the different factions in the Mojave Wasteland perceive your character. It is affected by positive and negative deeds that affect the faction in question, such as completing quests or killing members, respectively.

Reputation is separated into two categories: Fame and Infamy. Fame is positive and infamy is negative. Both types of reputation are tracked separately, the combination of which determines your reputation with any given faction. The benefits and drawbacks of any given reputation depend on the group itself. You may receive discounts with merchants, provoke attacks from hired thugs, or simply be treated differently.

Certain types of clothing or armor carry a faction affiliation (e.g. NCR armor), allowing you to impersonate a member of the faction the clothing belongs to. As long as the armor is equipped, the player's reputation will be reset to neutral for all factions. Instead, the player will be treated as a member of that faction, with whatever benefits or drawbacks that brings. Faction armor is not foolproof, however, as it will only work on common members of that faction. Officers, security guards and dogs will be able to see through it. In addition, faction armor will turn any opposing faction member hostile on sight, even if they are not hostile normally.

Reputation
Fame and Infamy (denoted 1 and 0 in the console) are earned by doing helpful or harmful deeds, respectively, to the faction. The combined effects of the two scales result in an overall reputation that is either positive, neutral, or negative. In the table below, these are colored green, black, and red respectively.

With a few exceptions, Fame and Infamy will only increase, meaning any positive or negative reputation with a given faction cannot be removed, only offset by a larger Fame or Infamy value. In other words, while it's possible to move from 'Hated' to 'Sneering Punk', then 'Unpredictable', then 'Dark Hero' by doing more and more good deeds while avoiding bad ones, there is no permanent way to move from 'Hated' back to 'Neutral' or from 'Hated' to 'Idolized.' Similarly, once a reputation of 'Wild Child' is earned, there's no ability to change it at all. Only three exceptions exist. The NCR and Caesar's Legion, two of the game's primary factions, will grant a one-time offer of amnesty for past misdeeds, resetting Infamy to zero while leaving Fame at its current level. Once this offer is given, any Infamy gained after that point is permanent. James Garret can be paid to start rumors in Freeside that affect your reputation with the town. There is no limit to how much this can be done.

Using faction armor, it is possible to gain a higher reputation than would be possible. Equip the armor of the faction you are trying to work with to reset your reputation to neutral. Then complete quests and earn fame which will increase from neutral and go up, but only so long as you wear that faction's armor.

Faction reputation
Each faction has a disguise which alters your reputation among other factions.

With the exception of the White Glove Society, Great Khans and Powder Gangers in Vault 19 all factions will attack you with a negative reputation. Additionally, Powder Gangers outside of the New California Republic Correctional Facility and the Powder Ganger Camp South would originally attack you even with a neutral reputation if you got too close to one, but this has been corrected in the latest patch to the game.

Factions provide the following benefits/consequences with adequate reputation:

Quest scripts themselves rarely grant infamy towards factions, but there are a few which do:
 * Failing Beware the Wrath of Caesar! gains infamy with the Legion and turns them hostile. Reporting to Colonel Moore or Mr. House that the Omertas have been dealt with in For the Republic, Part 2 or in The House Always Wins, respectively, or by completing both Wild Card: Change in Management and Wild Card: Side Bets, will cause the quest to fail, as will killing enough Legion troops (though this is a moot point since they will be hostile anyway).
 * Failing Don't Tread on the Bear! will gain NCR infamy, the amount and exact consequences depending on how it is failed. Reporting to Caesar that the White Gloves will or will not ally with him in Render Unto Caesar will cause infamy with the NCR and turn them hostile. Working with Yes Man or House will fail the quest, but the Infamy gain will be trivial and the NCR will remain friendly. However, all active NCR quests will be immediately failed, and it will be impossible to accept further quests from them.
 * Completing Back in Your Own Backyard in any way will result in Legion infamy, although this infamy is not enough to lower your reputation by one level on its own.
 * After completing How Little We Know by siding with Cachino and speaking to Caesar, you will be warned that further crimes against the Legion warrant death. Completing Restoring Hope, Oh My Papa by breaking up the Legion alliance, or I Put a Spell on You by siding with the NCR and speaking to Caesar after this warning OR speaking to Caesar again after failing to confess all crimes will result in Legion infamy and the Legion permanently going hostile. Note that certain scripts, such as Caesar's dialogue on House's death, will override his 'warning' dialogues.
 * Activating the self-destruct sequence in Hidden Valley gives you 100 infamy points with the Brotherhood.
 * Completing Ghost Town Gunfight will always grant enough Powder Ganger infamy to lower your reputation by one level. Killing any Powder Gangers during the quest will further increase your infamy.
 * Completing Beyond the Beef by tattling on the White Glove Society to Heck Gunderson results in White Glove infamy.
 * Telling Marjorie that you "eat people, too" will result in the White Glove Society infamy.

Towns reputation
A town's reputation determines your treatment by the townsfolk. Unlike factions, you cannot alter a town's reputation with faction armor. Towns will never be permanently hostile to the player; leaving the town for three days and returning should remove any hostility. Note: Script for Primm reputation exists within the game, but is not used. A mod exists for PC users to activate Primm reputation.

A positive reputation may yield positive dialogue, discounts from vendors, and even free gifts from wandering citizens. A negative reputation may result in negative attitudes by the citizens and higher prices when trading.

Specific consequences of reputation within towns include:

Scripted instances of town infamy include:
 * Lying to Lindsay about Mr. Cuddles results in Boomers infamy, regardless of whether you pass the Speech check.
 * Walking off during Pete's story in the Nellis Boomer Museum or condescendingly responding to his answers to your questions will result in Boomers infamy.
 * Completing Run Goodsprings Run will always lower your Reputation by one level in Goodsprings; killing townsfolk yourself results in further infamy.
 * Completing Beyond the Beef in a way which results in Heck Gunderson blockading food to the Strip will result in Strip infamy. Generally, this infamy would be garnered by tattling on the White Gloves and failing to pass the following Speech check.
 * Completing How Little We Know by siding with Big Sal will lower your Strip reputation by one level.

Bugs

 * It is possible that the game doesn't register taking off faction armor properly when switching directly to another piece of armor. In that case your PipBoy will still show your reputations as if you were wearing faction armor. This may lead to confusion when the player is being attacked by previously friendly factions. Putting on any kind of faction armor and taking it off again usually restores the players faction standing. Even if it gives you the message, "You are no longer dressed as a member of..." when removing faction armor it may not register correctly.
 * There is another bug that makes it when you equip a faction armor and take it off will reset that faction's reputation. This can be good in some cases, such as if you are vilified with the Powder Gangers and then equip and remove their armor then they will be neutral again. However, faction benefits, like the NCR Emergency Radio or McCarran monorail WILL be permanently lost. This can be very frustrating for players, as the reset seems it's not permanent. If you have completed all available side missions for the NCR or Legion, you cannot regain your reputation.
 * If the game manages to load a Powder Ganger while the player character has neutral or negative reputation, then that non-player character will permanently remain hostile, even if they respawn and the player character later gains positive reputation. Additionally, the Powder Gangers at Whittaker Farmstead will be hostile regardless of your Powder Ganger reputation; however, killing them does not seem to affect your reputation.
 * A Negative Reputation With the NCR—They give you 3 days to remove your negative status. If you wait 24 hours in the same spot after they've warned you, interacting in dialogue with them each day, you may find their dead bodies randomly in front of you when judgement day comes. How they were killed is unknown.
 * A Negative Reputation With the NCR—NCR Rangers have been spotted inside Vault 34 during the quest "Et Tumor, Brute?" possibly attempting to warn you about your bad reputation (or killing you). They'll engage in a battle with the feral ghouls of the vault before attempting to interact with you.
 * Encountered a bug where Legion were hostile no matter what even though reputation with them was either liked or idolized. DID NOT have Boone as a companion or even have him recruited, nor was any faction armor worn. Work around: thankfully this reset after completing Ring-a-Ding-Ding!, although dogs sometimes still turn hostile for no reason forcing the player to sneak attack them when this happens to maintain reputation. This may have been possibly caused by previously wearing another faction's armor and upon removing it the disguise was not properly removed which is another known bug.
 * When loading after gaining infamy it is possible for the game to retain the dejected face from infamy gain, with no text next to it, until you get another HUD notification in the top left.