Is it normal to feel ashamed of sexual attraction towards a subpar-looking girl

It's not that you are shallow, you just have some insecurities about what other people think. And so does almost everyone else. A wise man once said:

"It is only when he loses his fear of disapproval that a boy becomes a man. It is only when he loses his desire for approval that a man becomes free."

For me personally, there are plenty of women out there that I am sexually attracted to and would sleep with, but that I don't find attractive enough or interesting enough to date or be in a relationship with. This is totally fine. You can allow yourself to fully enjoy sleeping with women that you wouldn't date. Just don't make untrue promises to them about your intentions.

Imagine being in public with her and feeling totally good about yourself and what you are doing. Feel how freeing it would for other people to see you and for you to not have any thought whatsoever about what they are thinking about what you are doing. It might take some practice, but try to work on letting go of the emotional negativity that you feel when you think about people judging you for being with a woman that is supposedly less socially acceptable for you. Be free of it and you and her can enjoy each other as you wish. And you should know, there are a lot of men out there that are attracted to "fat" girls or older women or whatever and really like them. It's completely normal. Be yourself and do what you like.

Sounds shallow to me
why not try dating someone your very attracted too? Even if they wernt super attractive looking but I was attracted to them id still date them...I meen who cares what other people think?

It come from being an incredibly shallow human being.

Okay. I understand you, but you're going to HAVE TO bite the bullet. As someone who is ONLY attracted to overweight men (and thus has only dated any for the last eight years), I know ALL ABOUT the judgment, stares and snarky comments that come with dating someone people don't think is "hot enough". People who think you are shallow about fearing this have never undergone such a pain.
HOWEVER, you need to do the right thing. If you are public with this girl you are attracted to and like you will have GREAT TIMES and GREAT SEX which will outweigh the embarrassment. Also, having a SECRET lover always turns to shit and NOT being with the girl you like will be shitty as well. Just do it.

If you really like someone your friends and family will see those qualities you find attractive in her too. Don't let fear of what others will think of you, to stop you from pursuing a relationship with someone. You'll miss out on a lot of amazing friendships and relationships if you let others perceptions control your life.

This reminds me of when I was a child in primary school. This girl, who was my "friend" (I was a lousy one to her) wasn't popular, good looking, and generally most didn't like her...Sounds nice I would befriend her, right? No...We would walk to school and eery time before we got to school I would tell her to walk infront of me and get to school so we aren't seen walking next to eachother...I was so oblivious to the assholeness I displayed then. Lol.

Those are the best kinds of girls lol. The ones that don't know that they're attractive. The ones that hold your attention but you can't figure out exactly why.

Kids will be kids

now you know how bad girls feel

Why do you care about what other people think ? If you're a 15 years old cool kid don't answer... Otherwise,why ?

I don't get it. Do you think she's ugly or attractive?