mfwb 

Monogamous Friends with Benefits. .
So you're having sex with a friend but only that one friend. Generally this is an agreed upon situation by one married person and one single person. The married person may or may not be having sex with their spouse. The single person feels better if it's M-FWB. Otherwise, they'll assume you're banging half the city.

"I'm having sex with Cindy from accounting"
"She knows your married, right?"
"Yeah, it's a MFWB thing so she's cool with it"

mfwb by I won't tell. March 30, 2018

MFWB 

Made Fart With Butt. The act of making a fart with one’s butt.

As the terrible aroma began to fill the room, it became abundantly clear that Alex had indeed MFWB (Made Fart With Butt).

MFWB by Dr. Corn September 5, 2021

MFWB 

When you "Make Fart With Butt".

I MFWB'd so hard next to that girl.

MFWB by jakegrealg July 30, 2020