I have stories from both sides of the issue. The following is an old one where i was guilty.
When i was like 16 or 17 and little bit before and after that, i used to hang around lots of different guys from school. We used to go out in large groups, and we'd do the dumbest things we could think of. I did a lot of pathetic things in that period.
One phase we had at some point was to slap girls on their butts while driving through the city. Whenever one of the guys slapped a girl, i'd cringe. While i didn't reflect much on how the girls would feel, and while i didn't particularly view it as a big deal at the time, i felt it was uncalled for. I usually made jokes about how we're losers and that what we're doing is pathetic, but never objected seriously. My personal codes then were very low in regards to what harm i would allow to bring on myself, but were considerably higher than that when it came to others. I was usually the guy who never instigated things, but reveled in harming others when they instigated things with me.
Anyway, i never volunteered to do it, but one time everybody egged me to, so i got my upper body out the window and got ready. When it was time to do it, i froze and didn't do it. In attempt to diffuse the certain backlash of jokes from everyone i was with, i slapped a guy instead. He was dressed in a suit and looked real sharp, and was with another guy and a girl. He laughed when i did it. It worked in diffusing any possible backlash.
Besides the obvious elements about why this was wrong, there were also other elements. Like how everyone would avoid slapping a girl if she was dressed modestly according to the common standards, but would totally get excited and do it if it was a girl that dressed less than so. Also, as far as i recall, almost everyone seemed to feel guilty about it in some way or another, yet not once did anyone object or advice the others to refrain from doing this, me included.