Psychiatrists are called shrinks as a result of a comparison made between psychiatrists and head-shrinkers.  Back in the good old days, head-shrinkers were the tribal members who shrunk the heads of their enemies after killing them.  I guess both a psychiatrist and a head-shrinker screw with your head, in a way.  It’s just that one tries to help you, and the other one kills you and physically shrinks your severed head.  But, I mean, I guess I see where they’re coming from…