My JCP Ozzy will do this occasionally, but normally under the following circumstances:
1) He needs a good grasping point to explore/try to escape
2) He smells a potential food source/dangerous creature (i.e. one of our cats)
3) He is irked at me/at the house/at life in general

Granted, he is a somewhat cranky guy to begin with, but he has only bitten me once outside of his cage in the year since I've had him, and that was completely 100% my fault. (Here's a tip: When demonstrating what kind of movements would aggravate a snake to get it to strike, the snake will
probably strike.)
Admittedly, I tell everyone that he is bitey, but he hasn't tagged me in several months. The more you work with them, the more comfortable they feel as living bracelets/necklaces, and the less likely they are to get nervous and hurt you.
Best of luck!