Well, there's your problem right there. You should have a decided lack of urge to share anything with your parents about flirting with anyone. In fact, it's usually an urge against ever sharing anything about one's sexual urges with one's progenitors. Even amongst ostensibly normal heterosexuals.
Oversimplification and forgetting of the lives of humans FTW. To get slept with or knocked up, a woman merely has to catch a guy's eye and be receptive, which, even then, is not always so simple as just being genetically blessed to be smoking hot. To actually have a relationship, a woman has to somehow keep a guy's interest.
Someone who's vapid and slutty and relies solely on looks to get attention... Well, for one thing they're likely going to be bad in bed if they have that kind of attitude about interpersonal relations, being more of the lay there and take it like a dead frog variety. Two, most of the people who see this and proceed anyway are going to just play the use for sex angle. Which has a fair bit of overlap with that set of people who don't care if one's partner is just laying there like a dead fish.
Y'know, that whole thing evolutionary biology thing people referencing. Where the women want one mate to stay loyal to them to provide aid and resources for the young, while men have the opposite drive to have as many mates as possible in order to maximize number of offspring at a go.