laying an egg 

to poop your pants; to fart; a stinky bowel movement.

"Jingle bells,
Batman smells,
Robin laid an egg"

Clearly, by "laying an egg," the writers of this song meant that Batman was smelly because Robin had shit his pants in the Batmobile.

laying an egg by Solid Steak April 17, 2007

Laying an egg 

The act of pulling one of your testicles up to your ass and showing it to someone while simultaneously mooning them.

I just laying an egg(laid) in front of greg over there and he’s crying now.

Laying an egg by Vinny2444 January 6, 2022