I don't think the mockery received by the OP was okay, so no, that wouldn't be okay either.

Having said that, firstly, understanding why a bad behaviour happens is important in stopping it: maybe students should meet their roommates earlier, or get introduced to them over the phone, or get pamphlets titled "How Not To Alienate The Person You Will Live With For The Next Year", or something.

Secondly, the OP is talking about people who were raised in a totally different culture. "Black" in the context you're talking about presumably means black Americans, who live in the same country as you, speak the same language as you, and get the same TV as you. As someone from outside America, I'm quite happy that the cultural differences between us exist, because they make life interesting - however, they can be an obstacle to communication.

Let's use the equally arbitrary "Finnish Litmus Test": In the group text they joked that I would go out and play ice hockey all day, only listen to death metal, eat exclusively pickled fish...

Just sounds funny to me. Almost like a history of oppression is an integral factor in this, and joking about the diligence and work ethic of a group that's found huge success via those is different from joking about a group that's been literally enslaved, marginalised, and overtly oppressed by the group the jokers belong to.