There is a point where a troll becomes disruptive and you do have to ban them.
The mods have been pretty good about discerning when that point is reached. Sometimes right away, sometimes when we are invaded by trolls from another board, sometimes after members have chewed them up and spit them out.
The presence of pie and kitty posts are a good indicator that a troll is wearing out his welcome.
Bottom line: If a troll upsets you don't let him get you angry. Instead of anger, respond with Humor. If lacking in humor, search Bing or Google for pie and kitty pictures to post.
If you see a particularly witty response to a troll, Hi5 that poster. Reward good behavior.
Life is 10% what happens to you, and 90% how you react to it. Choose to react the way you want, now how the troll wants.