The target is usually a corrections officer who gets too close to the food slot of a cell door, but occasionally an inmate who really wants to cause trouble will target a food cart. But they do. The inmate's foot or hand might get caught in the cell door when it closes.
Inmates have other tricks to relieve their boredom.
Or they will pester the officer with requests to see a doctor, nurse or chaplain. It changes you as a person, and most of those changes aren't very nice. They are responsible for giving inmates mail and food, overseeing distribution of medication and escorting inmates to their visits. They inspect the cells and make sure inmates keep the area clean. And they count the inmates.