What is the Full Form of LMFAO ?

LMFAO - Laughing My Fu**ing As* Off

It is an Internet slang, used in a chat-based conversation like chatting, instant messaging, SMS, email, text messaging etc. It is used to represent something really really funny.

Like in a conversation :-
Person 1 : Hi
Person 2 : Hi! Buddy, wass up
Person 1 : I just got dumped
Person 2 : LMFAO