he also seemed to have an extra hatred for women considering he stabbed Cecilia in her groin and shot Betty Lou 5 times while David was only shot once. I wouldn't be surprised if he was a virgin and this "getting your rocks off with a girl" line from the z408 was just his way of masking it. he was fat, short and nerdy looking, I doubt any girl had slept with him.
I'm not sure we can say he had any special hatred for women. Cecilia was panicking and struggling because she saw Hartnell getting stabbed. He played dead, but she didn't. David was shot once in the head (first, I'm sure, to neutralize the bigger threat, the male), but Betty Lou tried to flee, so he shot until she was subdued. Since it was a .22 (small rimfire caliber) and he never hit her in the head, it took 5 hits.
Also, there's evidence indicating he was not short. The two people who were face-to-mask with him at LB indicated he was 5'10 to 6'.