Bean
To leave a large pan of cooked beans on the floor in front of an enemy's dorm room door. When he/she opens the door, they accidentally step in the beans. The person who committed the beaning peers around the corner and laughs at the beaned victim.

Baked beans are the beans of choice for the act of beaning, because of the thicker, brown texture of the bean juice, which leaves a lasting odor and/or shoe stain. However, others work almost as well if baked beans are not on hand.
"Dude, what happened to your shoe?"
"Someone beaned me when I was on my way to class."