A shortened version of the phrase "Don't Fuck My Tities," which is commonly said when you don't want someone to bother you because you have recently been upset by something serious.
1: "Dude, I got an F on my math test, DFMT's right now."
Down to fuck anything that walks. A ridiculously horny mindstate in which someone is willing to have sex with just about anything at anytime, anywhere.
"Dude, you haven't gotten laid in months. You must be DTFATW."
"Of course, I'd even do that 400lb'er over there."