Acronym, derived from LOL (laugh out loud) LMAO (laughing my ass off) and ROFL (rolling on floor laughing).
LMAOROTFLBTCSTCNDBFOOTWI FOAGWLLBGWTHROOTSAIAKBAYB: Laughing my ass off rolling on the floor biting the carpet, scaring the cat, nearly dying by falling out of the window in front of a guy who looks like Bill Gates, who then horrified runs out on the street and is accidentally killed by a yellow bulldozer.
Bob: So then I says 'that's not a cow, it's my sister!'
Sam: omg... LMAOROTFLBTCSTCNDBFOOTWIFOAGWLLBGWTHROOTSAIAKBAYB
South Central Los Angeles, California. Made famous by west coast gangsta rap of the early 90's for it's high crime rates and drug use. Artists like N.W.A., and especially one of it's former members, Ice Cube, often gave it a shout-out.
Also, was the target of C.R.A.S.H., the codename for a large amount of sweeps and busts by the LAPD aiming to clean up South Central.
"How to survive in South Central?/a place where bustin' a cap is fundamental/no, you can't find this shit in a handbook"
- Ice Cube, "How to Survive in South Central"