I went out with one chick who almost wouldn't let me hit the kitty. She was afraid it would make her fat. Not preg, FAT! She read that vaginal sex stimulates the womans body to prepare for pregnancy and would cause weight gain, widening of the hips, ect.
I never tried to convince her otherwise, and found there were plenty of pleasurable things to do with/to her. In fact, I think she found having the kitty pummeled was less than ideal. This from a woman who didn't like to finish a blow job!