Extra Chromosome

Alright, listen up, buttercup. This joke is about someone hitting back at an insult. Someone calls the person "ugly", and the person fires back by saying the other person is as ugly as an extra chromosome. Extra chromosomes are often related to genetic disorders like Down syndrome, which, like, isn't something you should joke about, but the joke is about calling the other person ugly, too. Which is also mean. You people should be nicer to each other, you hear?