ew tapping the mouth? I mean I could see how that would work but I wouldn't want to do it! And covering their mouth doesn't work either

i've tried that one!
For me, counting down from 5 works. Gets him to eat when he's being stubborn, gets him to go potty when he's being a turd about it, gets him to stop crying when he's faking it.. just took him a while to understand that when I got to 1 I wasn't playing around anymore.