I don't think anything is as bad as inquisitors. They don't usually come into my lands since I keep heresy down and the pope happy, but when I started taking territory from the excommunicated Venetians, there was an inquisitor in there who just won't leave. About every third turn he'll decide to burn someone. I lost one general before I spammed enough priests in the area to keep him occupied. If I can get a free turn without a Venetian army to fight, I'll squash him with the surround exploit.