-insult for a long post
-compliment for an humorous post
-acknowledgement of a strangeness or weirdness of a post
-irrelevant response to an uninteresting topic
-can be added to a post to imply raunchyness or cheekiness
The origins of the phrase is believed to the forums of the Sherdog BBS, more specifically the Off Topic forum, which has spawned the TL/FWI group (AKA The TL/FWIlluminati) in the Spring of 2006.
The group claims to promote for general random humor and moments they define as "WTF?" moments. They browse boards across the internet conversing, creating, and pointing out these poignant moments with their group slogan "TL/FWI".
The actually meaning of the phrase "TL/FWI" is supposed to be a closely guarded secret, known only by the higher level members of this group. They've adopted the surname "Illuminati" to reflect this element of secrecy.
Also popular amongst the group are disturbing images, various pornography, and Danny Glover.
"That's def. TL/FWI"