Lie Down With Dogs, Get Up With Fleas

     If you associate with bad people, you acquire their faults.

His Bark Is Worse Than His Bite

     Uncle Bob's bark is worse than his bite.  If I tell you this about Uncle Bob, what I mean is that his threats are worse than his actions.  It really is a reassuring statement because if you use it in reference to anyone, you are saying that they are really not as unpleasant as they seem.