According to psychology text Sticks and Stones, people feel shame when you remind them of something they are insecure about.   It's impossible to shame people in the bringing-things-up sense without this.  No one ever made RamblingMutt feel ashamed by calling him a furfag who wears diapers.  Deep down, Schumer doesn't actually like being fat (what human normally would?  Being her size is a massive health risk), so she doesn't want to be reminded of it. The second factor is that Schumer is a venal hypocrite.  She can't stand being called the same things she calls herself.