Pete Wentz simply can’t help not showing off his underwear … Every time he smells paparazzi around him, he lets his pants go down.

Why? We can take it like a “Kiss My Ass” advice, but I say he likes the photographer, and invites him to a “Menage a trois” with Ashlee.

The young couple was caught at the Musical “Wicked” on Hollywood Boulevard with that black apartment-car.