When a girl peels back her labia so that the peestream doesn't get misdirected by the meatflaps. Can also be used to describe a male sliding back his turtleneck.
Yalea peelback when you smell a horrible smell coming from your partners vagina or anus while doing doggy style and your lips involuntarily peel back over your upper and lower teeth.
Lou's girlfriend offered to give him a hand job while driving home from the party. She whipped out his throbbing hard cock and gave him a Ripe Banana Peel Back.