Foob being a combination of food and boob, the Foob Theorum is the idea that when a girl wears a low-cut top food will always fall between her boobs when trying to eat.
Jenny- "I was eating popcorn last night at the movies, and I got a bunch down my shirt."
A meme created by a lovely person that goes by the name Momma Peachu. This was accidentally while trying to say the number "Forty four" or the number "Forty five" one day, but messed up and said "Forty foob" instead. Saying this, her entire discord server started roasting her for saying it and repeatedly said "Forty foob" to the point where it became a meme.
Person 1: Bro, you just said "Forty foob" you're going to be banned chief.
Person 2: She'll get that it's a joke xD rofl haha