The sexual act of defecating in another's mouth while one wears a Tuxedo, or other formal wear.
"Babe, I got out the tux!"

"Oh boy! Get ready for Formal Brown!"
by Cuck80085 August 06, 2021
Get a Formal Brown mug for your Uncle Trump.
(verb ) To defecate in a partners mouth while wearing formal wear preferably a tuxedo.
Hey Daniel wanna formal brown later?

Me and Debora formal browned last night.
by ID production crew July 31, 2021
Get a formal brown mug for your dad Manafort.