I’m not going to defend the implication in Shagnasty’s post that he thinks he did nothing wrong - though the post is in a “pranks gone awry” thread - but the 17-year-old Shagnasty is presumably not the same person as the adult one.
When I was about 14 or 15, my buddies and I attended a youth club had a game called “squeeze the tit”, where we chased girls around and, if we caught them, squeezed their tits. It was wrong - it was sexual assault - but we did not know at the time, and nor did we have the empathy to realise the distress we were causing. Eventually, after one girl stopped attending for a few weeks, the penny dropped, and I personally felt absolutely dreadful about it.
I would never do that again (without consent!). I am sure that Shagnasty regrets his participation in a version of sexual assault too (not rape - he says they did not perform intercourse). Perhaps his apparent lack of contrition is because he’s rehashed the story several times.
If it is purely a fantasy of his, well, it seems he’s not alone - it’s the plot of the misogynist Roald Dahl short story Switch Bitch.