Take something the person uses like their glasses or something you won't completely ruin, and make jello! Put the item in when the gelatin is just starting to set, then finish letting it cool once you slide the glasses or whatever in!
Fake doodoo. Step 1 take a empty paper towel roll. 2 wet it under water til mushy 3. Break it into chunks 4. Form into cylinder shape 5. Set on side of toilet or in it. Works every time if u want to hear a scream lol
If you have a scale that isnt digital, you can turn the dial to ten so when they step on it, itll look like he/she (funnier if its a she) weigh ten pounds more :) (hope they dont look at the scale before they get on)