When you want someone to shut their whore mouth so you want to insert your big toe in their mouth to shut them up, but that wouldn't be publicly appropriateso you say "suck a toe" instead.
To tell someone to suck a toe, is essentially the mash up of “fuck off” and “kiss my ass”, in a much more PG way, and is much more socially acceptable in an environment with slightly less than chill adults.
Guy 1: oh my god, why would you stab my hand with your pencil?!
Guy 2: I’m sorry man, I didn’t see it there.
Guy 1: Jesus dude. Go suck a toe.