its an acronym used in texting. it stands for "text me the fuck back!" it can be used if someone hasn't responded to one of your texts in a long time.
"dude jake hasn't responded to my text and its been four hours"
"just send him another text saying TMTFB!"

*texting conversation*
Katie "Hey whatsup"
John=no response
Katie "TMTFB!"
by bossman773 November 3, 2009
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