Intravenous

Pass out from drinking too much.

Kill 3 (or more) enemies with a single frag grenade.

You must really enjoy pain. Finish the game on 'Masochist' difficulty.

Have a flashbanged enemy accidentally kill his own friend.

You really enjoy listening in on private matters, don't you?

Kill someone with the shrapnel from a frag grenade.

Complete the level "Steve's House" without firing a single shot.

Complete a level whilst using naught but the Taser.

Complete the game on the 'Easy' difficulty.

Complete a level without being detected.

Bait an enemy with your microphone, then take them out.

Unlock all unique weapons.

Complete the game with ammo auto-grab disabled.

Complete the game without killing a single enemy, unless when forced to.

Kill yourself with your own frag grenade.

Have your frag grenade shrapnel kill you.

Complete a level without saving once.