4) Made To Fuck Characters Are Not Interesting

Well, they're not.
This goes for cat people as well, and most of those below. As soon as you make a character's sole purpose to find a mate, or find lots of sex, your character is not interesting. Sorry. I'm not saying it's bad to be sexy. I'm saying it's bad to focus only on finding people for your character to have sex with, marry, and/or have babies with- to the exclusion of all other interaction.

This is what I call 'Dragonfly Characters'- they're made one day, that same day they find everlasting love with whichever corresponding Dragonfly of the opposite sex happens to be around, the next day they get married, the day after that they have kids, the day after that they get bored and commit dramatic suicide.
Yawn.
It's just not interesting. Try to at least PRETEND they have some other purpose to existance- or perhaps, if you really want, give them a damn good reason for being such a nympho-or-matro-maniac. Do they need constant reassurance? Are they actually really insecure? Do they have big Oedipal comlexes? It's fun to get really Freudian here.