i'm gonna eat your foot - A promise that your foot will be the first thing to be taken

A promise that your foot will be the first thing to be taken, and you won’t be able to stand up again.

I'm gonna eat your foot if you don’t stop bugging me about my homework.

I'm gonna eat your foot if you keep making me do your chores.

I'm gonna eat your foot if you don’t stop talking about your stupid crush.