1. To renege on or break a deal based upon previously unexpressed or recently invented fine print, often due to unforeseen negative consequences.
2. To promote one's own self interest to the detriment of someone else to whom you have some type of loyalty or obligation.
1. Every time we make a bet, he jews out of it when he loses.
2. I'd ask him to join our group, but he'd end up jewing us over when it comes to the final grade.