They do happen, but you're right they're usually centered in bigotry. I think "banged your mom" is more of a dominance play, as iirc there have been times where women have used "I fucked your dad last night" in a similar way, but it strongly skews the other way due to toxic masculinity and homophobia. Saying I fucked your dad last night as a man talking to another man would be suggesting the father is gay or bi, and that your yourself are as well.