shits and giggles

For the hell of it

Dave: Dude! Why'd you draw a dick on the principal's mug?!
Sam: For shits and giggles.

Shits and Giggles

Doing idiotic, childish, abnormal, or even just illegal activities for fun.

A: "OH MY GOD! WHY DID YOU BLOW UP GRANDMA'S HOUSE?!?"

B: "For shits and giggles :)"