The full form of LMBO is laughing my butt off
The meaning of the acronym “LMBO” or “lmbo” means the phrase “laughing my butt off.”

Origin of LMBO

The most likely origin of “lmbo” most likely came from the same origin of the more profane “lmao” meaning “laughing my a$$ off.” This acronym came about from the origin of the acronym “lol” meaning “laughing out loud.” “Lmao” started being used after “lol” to show that something was funnier and warranted more than a simple “lol.” This occurred sometime during the 1990s as internet chatting and text messaging were beginning to escalate in popularity as a form of communication. “Lmbo” most likely came about as a means for people who do not like to curse to say the same thing as those who were using “lmao.”

A text exchange between two friends.

Friend 1: Hey, I have a joke for you.
Friend 2: Okay, let’s hear it.
Friend 1: How do you catch a polar bear?
Friend 2: I don’t know. How do you catch a polar bear?
Friend 1: First, you cut a hole in the ice. Then you take some peas and you put them around the hole. When the polar bear comes to take a pea you kick him in the ice hole.
Friend 2: LMBO! That’s so funny!