Yeah, since the “social contract” is a concept, it will vary depending on what society or even part of society you’re in. The Paradox of Tolerance specifically refers to societies that value tolerance of others - there’s no paradox in a society that’s just fine with being intolerant. When it comes to “is it okay to punch Nazis?”, I’m of the belief that it’s highly dependent on the situation. If you’re meaning to just express displeasure in their ideology, the better way to do that is to collectively “show them the door,” make sure they know that their ideas aren’t welcome without resorting to violence. But actively oppose them and don’t simply ignore them, because they will use any power given to them to suppress others. If the Nazis are violating your rights, then, yes, it’s okay to punch them because they’ve taken a step over the line at that point.

“no paradox here, if you punch nazis, you are a nazi, because it breaks the social contract”

I’m pretty sure this is the opposite of what they meant because as I said, the Paradox of Tolerance only apples to tolerant societies, which the Nazis are demonstrably not a part of. And of course, breaking the social contract doesn’t necessarily make you a Nazi. Could you break the social contract in a tolerant society by punching a Nazi? Yes, if you instigated violence without sufficient reason.