Know what I hate? I hate the person who says "that's not funny" or does that fake "ha ha" laugh that implies the same thing. Humour is subjective, and if you don't think a joke's funny, just deal with it and shut your trap so the rest of the people can enjoy it. Because once someone says "that's not funny", it ruins the mood. At that point, I'm not sure who looks worse: the joke teller or the person who just killed the mood.

[I didn't recently have this done to me, but I have in the past. Just thinking back.