The Dirty Shot is one of the easiest ways to ruin somebody's night at a party. When you notice your rival has had a bit too much to drink, you replace his/her shot glass with one full of cum. Enjoy as you watch first looks of confusion and then looks of horror.
Bro #1 'dude did you see that asshole matt last night'
Bro #2 'ya i can't beleive that douche took a dirty shot'