Tomfoolery is foolishness. Starting a food fight in a cafeteria is an example of tomfoolery.
Tomfoolery is a silly-looking word, and it means a silly thing: foolish or ridiculous behavior. Tomfoolery is senseless behavior, like pulling pranks or being obnoxious. If a bunch of students in class keep talking and laughing, the teacher might yell "Stop your tomfoolery!" Tomfoolery can be annoying to others, but it's usually not serious. Committing a crime is a lot worse than tomfoolery. Tomfoolery is more like goofing around or being a clown.