Why Can't We Be Friends?

 is a quest in Fallout: New Vegas. It is given by Philip Lem or Samuel Cooke located in Vault 19.

Quick Walkthrough
You will need an Explosives skill level of 60 to destroy the caves or 50 to destroy the caves and the vault. The explosives can be placed on the uniquely shaped green microcline rocks. The C4 will react with a nearby pocket of Potassium which will destroy the caves and the vault.

Detailed Walkthrough
The player can choose to complete one of four options. Either to kill all the Fire Geckos for Samuel Cooke to help his gang create bigger explosives and join with the Great Khans, help Philip Lem seal access to the cave surrendering the convicts to NCR OR joining the Great Khans (Speech 60 required), blow up the mines and Vault 19 killing everyone. After talking to Lem in the Overseer's Office, and talking to Cooke in the other Overseer's Office next door, go to the lower living quarters, there are a few Land Mines and Fire Geckos, so talk to your company before using the elevator, tell them to stay where they are so that they wont run into the mines, because they will attack the geckos (extremely recommended in hardcore mode, but see "Bugs" below for possible solution). From the living quarters find the common room with the pool tables and a hole in the floor. It will bring you down to the sulfur mines. On this floor are the Fire Geckos you have to kill to complete Cooke's quest option. On this level you will also find a rock formation with green crystals in it, here you can use the C4 to either destroy the mines, or the entirety of Vault 19.

Cooke: Join The Khans
After you have killed all the Fire Geckos go back to Samuel Cooke. He then sends you to the Red Rock Canyon to meet with the the Great Khans; where you have to convince Papa Khan to join forces with the Powder Gangers in the vault. After you have convinced Papa Khan, return to Samuel Cooke to finish the quest.

Lem: Surrender To The NCR
In the caves find the green crystallized rock. Here you can choose to blow the caves up (Explosives skill of 60 and 3 C4). Return to Lem and let him surrender the gang to NCR. This leaves the vault empty for personal use.

Lem: Join The Khans
Find the green crystallized rock in the caves. Here you can choose to blow the caves up (Explosives skill of 60 and 3 C4). Return to Philip Lem and convince him to join the Great Khans (Speech 60 required). He requests you act as a liaison, requiring you to visit Red Rock Canyon and talk to Papa Khan to secure their alliance. Return to Lem once again to finish the quest.

Blow up the caves and the vault
Find the green crystallized rock in the caves. Here you can choose to blow the caves up and the vault (Explosives skill of 50 and 5 C4). WARNING: This will fail the quest, and you will not earn any XP. In addition, you will be transported to outside the vault, where the Quest Failed message pops up.

Journal entries
For Philip Lem:

For Samuel Cooke:

Bugs

 * If following the Lem quest line, the map marker will tell you to go to the "Sulfur Caves" entrance (now blown up and billowing smoke) to find and talk to Lem about joining the Great Khans after talking to Papa Khan. Lem is actually located in the Overseer's Office, and if you've opened the stairs leading to the sulfur caves he can sometimes be found stuck there.
 * If you enter the Overseer's Office from the elevator entrance (Hard Lock) in Sulfur Cave and open the Overseer's Office with the Average Terminal, or just go through this route at any time, you may have some issues with your companions as mentioned above in less detail. When you ascend the stairs into the office your companions become confused and instead of following you up will run out the door back into the caves. If you are at the top of the stairs with a companion and run down they will run back into the vault. It is possible, however to keep your companions with you during this if you manually "push" your companion up and down the stairs. Just crouch and slowly move them and they will glide up, or down the stairs from your push.
 * If the player chooses to destroy the sulfur caves and the vault, but didn't kill Cooke personally, then the ending sequence will still show Cooke still alive and the Powder Gangers terrorizing the Mojave.