I don't have many guilty pleasures these days not because I don't misbehave, but because I don't feel guilty about them, heeeheee. (evil cackle) Mostly, I just eat more than I should, or eat all the wrong stuff, like ice cream, and such.
When I was a kid though, I had lots of guilty pleasures. Most of them had to do with getting my two brothers in trouble, or doing stuff that annoyed them. Needless to say, I learned to run really fast, really young. There was one thing that I did only once, that I would have loved to do over and over again, but I didn't want to become my brother's murder victim.
My oldest brother was impossible to get out of bed in time to walk to the school bus stop. It was a mile and a half, and we had to be there by 7;30am. Anyway, I called him a few times, this one day, and he ignored me, so I went into the bathroom, and filled a big fluffy wash cloth full of ice cold water, then I rung it over his face. It took him something like two seconds to jump out of bed! Luckily, I had a lock on my bedroom door, or he would have strangled me.
Another guilty pleasure was taking strawberries from a neighbour's garden on the way home from school. The garden went right up to the edge of the road, and all the kids helped themselves in June, when they were in season. I only remember the garden being there for a couple of years, so he must have moved the garden, or he stopped planting one.