Gabrielle Union: Don't Be Ashamed to Eat Butt

"So, how old were you when you first ate a butt?"

That's a real question Sway asked Gabrielle Union during his radio show in a conversation about sexual reciprocity ... a conversation that has everyone grabbing some Scope.

Gabby appeared on "Sway in the Morning" and talked openly about sex -- and that's when tossed salads appeared on the menu.

Dwyane Wade's wife says even though men will deny it, they enjoy a little backdoor love from women ... and they're singing a completely different tune in the bedroom.