Acronym for Thank god it's Monday night football, the use of which will probably earn you a high-five from some college guy who is most likely way to old to high-five.
"Dude, I had such a shitty day. My wife divorced me, my kids took all of my weed, but hey, TGIMNF."

Random Monday:

Guy 1: "Hey dude, some ugly chick wants me to go out with her tonight. What should I do?"

Guy 2: "Just tell her you have an important business meeting at my house."

Guy 1: "Ahh, good plan. TGIMNF."
by Stevie Weevie OT October 6, 2010
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