Running into a man and dropping your things as a result. Mark Sanchez is prone to assfumbling, but an assfumble can happen on the street. Walking into a man and dropping your bag or running towards the line of scrimmage and hitting your offensive lineman in the ass, fumbilng.
Football Example: Mark Sanchez has the ball, he makes contact with his lineman, assfumble! Patriots have the ball! Patriots have the ball!
Everyday example: Man, I was walking to the store when I ran into a guy and totally assfumbled my phone.
The first time a girl ever sticks a finger up your arse when she is slopping away at a blowjob. One's reaction is initially "WTF ARE YOU DOING?" but in just a few seconds, one will be on a different plane of existence.
A friend suggested that I pick up this CD. After a long day of work, I put this in and, on the first listen of the first track, I yelled "WTF WAS HE THINKING?!!?!". But by the time I was finished with the second track, I think I 'got it'. This album is definitely an assfinger.
A staked finger with quills protruding and extending from one's asshole. Stinks a bit. An assfinger noogie stings a bit but makes you ejaculate violently.