Cold spagetti at the foot of the bed under the covers is good. You have to place it where the persons feet will hit. You dry off the spagettie as best you can but still keeping it cold and clammy.
Crisco on the toilet seat.
We did tons of pranks when we were kids. I owned fake barf and fake poo when I was like 10. I got lots of use out of those. Fake barf at school was soooo funny.
I had a co worker that was deathly afraid of mice. I colored some dry rice with black marker. Looks just like mouse poop. I spent two weeks setting the scene by laying out bits of "mouse poop" on his desk and around the office. He was getting so paranoid. I then bought a baby rat and put it in his desk. He just about knocked everyone over getting out the door. The joke was on me as we ended up keeping the rat as a pet. It was worth it.