The O-Face is the hilarious face you make when you reach orgasm.
The term O-Face is generally credited to Mike Judge, who used it in "Office Space". The character Drew (pictured above) is talking about picking up chicks, and the following exchange takes place:
The O-Face has since been subverted by Three Olives Vodka for use in their ad campaigns.
1. The Pirate
2. The Birthday Cake Blow-Out
3. The Intestinal Distress
4. The Monkey
5. The Wargasm
6. The Special Olympics