When a girl or woman has spent way to many lonely nights on tumblr. Alone. And she has taken on tumblr as part of her personality.
Guy 1: Hey man look at that chick over there! She's got a mean case of the tumbles.
Guy 2: Hey chick come over here!
Chick: Oh my god guys, did you see that (insert band name here) in concert?! They are just sooo perf, I can't!!! asdfjkl!
Guy 2: Oh god...
Drunkenly falling out of bed before or during the act of sex, thus ruining the moment.
So he tumbles outa bed so hard and fast we just couldn't do it then, poor fella hurt himself too