randomly choosing a random outgroup to collectively hate must be ironically funny sometimes(see: jokes about the fr*nch) Genuinely there is no other reason. sometimes people will create justifications/other explanations for it but really its just absurdist humor with a pinch of tribalism. edit: i should add though, usually this type of humor is meant to be ironic by most of its participants. the more i think about it, the more it seems this is more rude than funny.