Mentioning X friends works best if I'm not perceived as doing so with the intention of establishing my credibility as a non-(X-hater). But with that proviso, it can work pretty well.

Also, for iterated discussions, it can sometimes help to establish a practice of preferentially using groups I'm actually in as examples of negative traits, and only using groups I'm not in as examples when I genuinely am claiming that my groups don't have those traits. (It's important when using this approach to avoid being seen as "self-hating" though.)

Of course, if I'm in the position of genuinely believing that group X is either generally inferior to my group, or inferior in certain specific ways that I genuinely consider more important to discuss than other group traits, that's less available as an option.