This saying is originally from a rather obscure meme that includes Max and Ruby. At the end of the comic, Max exclaims "BEEP BEEP LETTUCE" in response to a question Ruby asks.

Essentially, Beep beep lettuce can be used as an interjection whenever one feels it's appropriate or just want to mess around with whoever they are with.
Person 1: Just grab me the Ragu from the stock room, ok Jimmy?

Jimmy: BEEP BEEP LETTUCE

Person 1: ...
by serialspongedesecrator September 16, 2017
Sounds like the japanese phrase "ビープビープレタス" which is pronounced be-pube-puretasu which sounds like beep beep lettuce. It means "your eyes are stars"
by Estrobe March 8, 2019
the love of my life also can be altered to make beep beep communism.
guy 1: wheres all the food gone

guy 2: beep beep lettuce
by man wit da plan and a werd ta February 19, 2020
Beep Beep Lettuce
Mike: Hey Jim. Jim: Beep Beep Lettuce
by TriTimes December 12, 2018
Friend: Alright, beep beep lettuce!
Me: beep beep lettuce!
by hithereurbandiconary November 16, 2016