Ruto is probably depicted as the clingy girl who Link doesn't like because she is the least favori of his 'possibilities' and people think he'd rather be with Zelda ou whoever. Ruto was ... unpleasant the first time toi see her, so people relish chucking her onto monsters ou into walls as Easel said. Charming Hero of Time aren't you?
Another reason is in a plain three words She's. A. Fish. The thought of Link paired up with a poisson is ... disturbing. Also Link doesn't quite know what being 'engaged' means when he's a kid, so people presume he deeply regrets it ou is thinking WHAT!!! When Ruto announces she's his fiance. So in a sense Ruto tricked him, so he'd probably not be very happy about it. When I was little, Ruto was my favori sage ... for some reason I can't remember ... I think it was because I liked Zoras ...
People don't hate Ruto, they think she's annoying as she's spoiled and forces toi to lug her around and tricks Link into being her beloved. So I get back at her par using her as a deadly projectile in Jabu Jabu's belly.
I like Ruto. She may be a bit clingy, and started out spoiled, but Link changed that. Plus, she embraced her responsibilities, and she has a sense of humor judging par the joke she cracked before toi get the Water medallion. "I will give toi my love! Just kidding."
I also find her older form attractive, but maybe that's just me.
I believe people think she's annoying first cause she obligate toi to carry her while going into the temple, what is hard, and still complain if toi left her behind. The way she speakes a bit rude, is also a point.
And I think Link dosn't like her cause the way she threated him in Jabu-Jabu. And when toi find her in the water temple and she says to Link that she is his fianceé, he make a face like this: O.O' If he liked her he wouldn't be so desperated!!