Hit the Deck (Fallout: New Vegas)

Hit the Deck is a Fallout Tactics, a J.E. Sawyer's Fallout Role-Playing Game and Fallout:New Vegas perk.

Fallout Tactics
You react very quickly to the word "incoming!". Halves the damage from area attacks and splash damage.

Fallout: New Vegas
Your extensive familiarity with Explosives allows you to ignore a portion of their damage. Your Damage Threshold is increased by 50% against any and all Explosives -- even your own.
 * Actually, this perk is not implemented that way at all. Instead, any time you are equipped with an Explosives-category weapon, your current DT is increased by 50%. This makes Hit the Deck one of the best perks in the game for a character who makes heavy use of Explosives. (Patched in 1.1.0.285)

J.E. Sawyer's Fallout Role-Playing Game
You react very quickly to the word "incoming". When hit by damage from explosions or sprays, you are considered to be an additional 2 hexes away from the origin for purposes of determining damage.