What you demand someone does after they offer you food to ensure it is safe to eat. An especially good tactic when they did do something to it and they have to waste it.
Dude 1: Yo, you want some of this burger? I didn't do anything to it. *snort snort laugh snort*
Dude 2: Fuck you bro, take a test bite first.
Dude 1: Aww.