What is Surf's Up?
When you and/or a bunch of your friends piss/shit, pour bong water, rotten milk, anything nasty into a trashcan and lean it up some unlucky person's front door. You then knock on the door, run away and when they open the door yell "SURF'S UP!!!!"
Variation: Place a Ken doll into the trash can with a flag in it's hand reading "Surf's up!" so that it will pour in the house when the door is opened.
Yo this bitch pee'd in bed so I gave her the surf's up.