How often do you jerks get shit out of your bags

I do hate the jerks who steal the spot above your seat though. Had a bloke across the aisle, and a row back, put his bag in my spot once (and basically the whole cabin was free) because "he liked to have a good view of the spot his bag was". I then put my bag directly above him, and made a point of getting shit out of it multiple times not through need but just to wind him up