Tdtf is the abbreviation of “too drunk to fuck” (originating from the Dead Kennedys song).
This is used as an expression that you have really had too much to drink (or that you are literally just too drunk to fuck)
"Man, Get me out of here, I'm tdtf!"
"sorry I'd love to go back to yours but I'm tdtf!"
(Please note these examples are more coherent than you’d probably get if the person is actually tdtf!)
Too Drunk To Function.
liz: did you hook up with matt?
mary: nah dude, i was TDTF.
liz: damn, well better luck next time.