If you could have any superpower, what would it be?

I used to think I'd like mind control. Among my first uses of that power would be to make other drivers stop whatever idiotic behavior they happen to be engaged in (talking on the phone, driving about three inches behind the car in front of them, etc.). I'd also use it to make cashiers somehow find the strength to say "Hello, how are you?" or "Thank you" instead of >grunt< (which I think is "hi") or "yut" (which is "You're welcome. Have a good day."). I guess I'd just like to make people behave more kindly in general.

My brother changed my mind, though. When I asked him what his superpower would be, he didn't even pause to answer: The power to make people beat themselves up. I like this power even better than mind control and here's why: with mind control, the subject would be unaware of what's really going on. There is no lesson learned. It's almost like serving a jail sentence only when asleep. Making people beat themselves up is muscle control, so it's more of a punishment.

Let's look at an example. One thing that annoys me is people who talk very loudly in the library, especially when I'm trying to study. If I were to use mind control to make them quiet, they aren't aware that it's wrong to be quiet. From their perspective, they are being quiet of their own volition, unaware that there is anything wrong with talking loudly in the library. If, however, I were to make them beat themselves up, they would be quite aware that something is very wrong. They would likely wonder why they were beating themselves up. With great power comes great responsibility, of course, so I would approach them and inform them that the reason they are beating themselves up is probably because they were being too loud in the library. I say probably because someone else in the vicinity with the same powers that I have might have been trying to teach the same person a different lesson. Not likely, I suppose, but some people are practically begging to incur that power.

The disadvantage with this power involves drivers, who I want to beat themselves up more than any other segment of the population. However, doing that when they are still driving might cause them to crash, perhaps killing themselves and others. One would have to wait for them to stop at an intersection. Also, it would be much harder to inform them why they beat themselves up, a sine qua non of this particular power. Perhaps some signage could address that issue.

So I guess I'd take either.