LB simply stands for "Loose
Butthole". This can be used to describe yourself or other
people, and it'
s connotation depends on the situation at hand. Its meaning can be equated to "getting anally penetrated" or just being a sexually loose person. An alternate meaning could be used in the context of being recently bested by a person or task.
John: "Hey have you taken the chemistry test yet?"
Bart: "Oh my god its so hard. I'm so LB right now."
John: "Dude what do you know about
Jessica?"
Bart: "I heard she'
s super LB man go for it."
butthole loose