She can only have sex for purposes of procreation, Rick. Only in the missionary position, not allowed to move her hips or groan. Foreplay consists of the words, "Are you fertile," or, if you are feeling adventurous, "Hey, it's Saturday. Wanna do it?"
It's twisted and wrong, I know, but that's the way these people are. It likely explains why one of them was starting fights in Satarbuck's with Peapod's friends too. Pure sexual frustration tends to lead to violence.