When the excrement in one's anus cannot be contained any longer and it starts pushing open the sphincter. Probably related to childbirth where the top of the baby's head (the crown) is first visable as it emerges from the vagina.
"OMG I'm crowning so bad it's like I've got a turtle neck hanging from my ass..."
An exploratory sexual move on a woman, kind of like fisting, only using your head. Gives that bigger girl or post pregnancy shawty a real buzz and gives the dude a chance to look around and see the kind of place he came from.
Yeah man, I totally crowned Maureen last night, crowning is her biggest turn on.