I’ve tested this in a few subreddit situations, and so far, it’s been effective.
Essentially, you just have to remind them that there are guys who are better to women than them, and remind them that it is most guys. Most guys are better than incels. Don’t leave room for gray area interpretations- tell it to them straight. They need to know they’re the odd ones out.
“Interesting, most guys aren’t controlling about clothing. It sounds like most guys are better than you.”
“I’ve never met someone who thinks I need to have my snap map on at all times so he can monitor my location, nor have my friends dated someone like this, but maybe that’s just because most guys are better partners than you.”
“My fiancé/spouse/boyfriend has never thought he got to make decisions about my body and contraception, but maybe I’ve just been lucky enough to know and date men who are superior to you.”
If it’s a situation where they’re talking about their own girlfriends/wives/fiancées, I’ll say something like:
“Wow, it sounds like you’re really disrespectful with boundaries. I’m glad you’re ex is making a positive change to move onto better men than you. She’s going to be so much happier and she really deserves happiness.”
“You know, my husband and all of his friends are way better to women. It sounds like you need some better male role models.”
“You realize that most people are better to their spouses than you are to yours, right?”
I have LOVED hearing about guys who stand up to incels, because I think incels are more likely to listen to men than women. However, I think we make an impact when we remind them that their sexist attitudes are not normal, healthy or acceptable- but we have to frame it into a context they’ll care about: sexual competition.