Joking about stereoptypes like that is commonly considered simple bigotry, but all of you know that. Right?
Yes, we do. But you appear to be going by a set of black-and-white rules to reach your judgment and completely oblivious to the nuances of a community social interaction that remove bigotry from the equation.
Following that basic rule book for your own conversational style is probably your best course of action, given that you're not adept at parsing out context and layers of social cues. Passing judgment on people who ARE more adept at social acrobatics, that's not a good look for you. Scolding people -- when you've completely missed the point -- is just painfully awkward for everyone involved.
So here's the "advanced socializing" rule you're not understanding: In a group of friends who have known each other for years, who have a history of interactions and knowledge of each other on which to draw, teasing and joking have different boundaries from those of public statements among strangers. Context changes the meaning and significance of the interaction. Joking about stereotypes among friends
who actually belong to the stereotyped group is not perceived as bigotry. To be fair, it can be risky to do this if one oversteps shared boundaries or if someone is in an especially vulnerable emotional space that day. But because of our very long associations (some of us have been part of this community for over a decade), we can get pretty rowdy with each other and no harm done.
You're new to the community, and you're obviously not familiar with the dynamics at play. This is an excellent opportunity for you to learn, if you're willing to listen rather than preach.