Thanks for the reply, and upvoted. Now there are three things I don't understand ;-). It rings true in the sense that people can be reliably expected to behave that way. But I still cannot empathize, and if I have the same mental machinery as the booers, then I ought to be able to.

1. Fun to boo. This one feels right and yet so foreign. Shouldn't sympathy for the target of criticism kill the fun? Like you imagine doing something hurtful, then you picture the other person, hurt. Then you imagine what it would be like to be that person, and, jeez, I wouldn't want that! So I'd better be nice to them. (This is why I still can't empathize with cruelty. I can see hurting someone unintentionally, or when the stakes were high, but petty malice is so weird. What are these people thinking?)

2. Thrill of the crowd. Sometimes it's easier to go along with the crowd, like if everyone is doing X, then it's just simpler to do X than to do nothing. And sometimes you can use the crowd dynamics to get away with something you'd never do as an individual. But thrilling? Like a roller coaster, or gambling?

3. Anger. Sure, I've seen bad performances. But booing doesn't improve them; it only makes them worse for anyone in the audience that might be enjoying themselves. And it's almost never the performers' fault in the sense that they're doing it to me, so any anger would be misplaced. And even if I was actually angry with a performer, booing isn't the best way to take it out on them. It's just the most public way.

Then again, misplaced anger serves a useful purpose in some contexts. My buddy's sister gets a lot of good deals at stores because she verbally abuses the employees, and she does this not to get the deals (that would be sociopathy), but because she always perceives an insult ("Did you see the way he was looking at me?!"). Maybe it makes sense to have a general policy of getting "irrationally" angry sometimes.