Typical of situations wherein one is not attracted to a person physically or emotionally, but still partakes in a sexual act due to lust. Upon climax, when the hormonal impulse has been satisfied, one feels an overwhelming feeling of disgust and shame. Cum horror is often followed by post-sexual fugue.
Yeah we had sex, but I got a bad case of cum horror. I wanted to throw-up, so I just went to sleep hoping he wouldn't be there when I woke up.