When I'm being tailgated, I calmly slow down until the tailgater goes crazy. What little things do you do to punish people?

Today I was being tailgated pretty hard. I wasn't driving that slow either, it was a 35 road and I was going 40. However, apparently this guy couldn't handle that, so he started honking and tailgating me. He eventually went so far to scream "move it dick!" at which point I gave him a thumbs up and slowed down to ten miles an hour. Considering it was an incredibly twisty road and there was no real way for him to pass, he got pretty angry. Which was really fun to watch... for the next five miles.

EDIT: To clear up some stuff... the guy was driving a two seater. There was no sign of any sick or injured passenger. It was raining, and it very much flooded the shoulder. In other words, I couldn't pull over if I wanted to.

EDIT EDIT: As many people did point out in the comments, it is SAFER to drive slower if someone is tailgating you. (if you can't pull over) If there's a short distance in between the you and the car behind you, you should be slowing down anyway to give more time for a reaction incase of a sudden stop.