Can I ask a guy how big his dick is after he asks how much I weigh?
Are you comfortable being asked your weight?
No, it's one thing being in shape, it's another being fat
It's understandable to be irritated or hurt when someone asks about your weight, but returning verbal fire with comments on penis size isn't the way to go. Be the more mature person in the crowd and ignore him.
Someone can't ignore the question
They can ignore a question if they're uncomfortable with it, just tell him that you don't want to tell him how much that you weigh and that he is being hurtful. Don't lower yourself to his level by asking a terrible question back.