After many years of hiring, I've found one warning sign that tips me off to this type of behavior. If an employee complains excessively about his old/current company during an interview then he's likely to complain about his new company too.

In the three times I specifically remember the interviewee dragging his old company through the mud, they ended up being a "bad apple" within six months of working with us. If they're not tactful enough to sum up any old employer problems with a wry, witty passing reference, then you should be worried about how they'll act when they run into differences with the rest of your team.