Is it normal to joke about a toddler being sexually molested?

My mother keeps telling what she thinks is a joke about my four year old son. He's into dancing and singing and he's polite and sweet. He even looks like an angel, with big blue eyes and little gold curls. Anyway, my mother will "joke" that he's attractive to child molesters (how my mother would know what's attractive to a child molester is another problem entirely). She does this in front of me, him, and my other two children. It makes me sick to my stomach to think of, but when I tried to tell her that, she got mad, started screaming and crying and told me she didn't care.

Am I totally off, here? Is it normal to think that your child being molested is funny? Am I being unreasonable for not wanting to hear it and not thinking it's funny?