Some examples of killer comeback lines include to say that the 1880s want their joke back when someone tries to make an insult that implies that something is out of date and to ask if a person's mouth comes with a mute button. Other comebacks include to insult a person's appearance or his intelligence.
If a person says that the 1980s called and the 1980s want the haircut back, a killer comeback is to say that the 1880s called and the 1880s want the joke back. This works for any kind of insult that begins by saying that another time period called because something is so out of date. Alternatively, a person might try to insult someone's appearance by asking if his shirt comes with a dimmer switch. A killer comeback in this situation is to ask if the person's mouth comes with a mute button.
Many comebacks insult a person's appearance, such as telling a person that he could sue his parents for the way he looks. Alternatively, a comeback is to tell a person that his pants don't make him look fatter because nothing could make him look fatter than he already is naturally. Another line says that whatever look the person is going for, he missed it. One comeback that insults appearance is to say that when the person looks in the mirror, his reflection simply walks away.
To insult a person's intelligence with a comeback, one could say that he can't understand the person and that the person should stop speaking in the idiot language. A comeback could add that the insulting person really shouldn't worry because brains aren't everything, and in his case, brains are nothing. Another comeback about intelligence says that the insulting person proves that evolution can operate in reverse.