Die-hard Britney Spears fans are crazy!  They will ride for their girl, and apparently they will bite her too, if given the chance.

Brit took her 'Femme Fatale' tour to Rio, and as usual pulled a lucky fan out of the crowd for a lap dance.

What happened when she lumbered her way up the poll was definitely not part of the program.

The best part about all of this is that Britney's boyfriend, Jason Trawick, is currently on tour with her.  That means he was sitting back stage watching his girl get bit by some crazy fan!

There are also plenty of rumors running around that Jason plans on proposing to Britney after the tour raps up.

No matter what you think of Britney, you have to give her credit for being able to keep lip-syncing after this kid snaps at her.