A Chocolate Chin Strap is like a Blumpkin for a girl. The male applies the mouth to the females vagina. Once there he starts eating her out while, the female is taking a shit. Once this action starts her shit then leaves a tiny chin strap appearance on your face.
"Dude whats that brown stuff on your face?" tom says.
"Not much man just my Chocolate Chin Strap, from my girlfriend!" john says.
"Damn that bitch is sick and so are you!" tom says.