I think a lot, perhaps the majority, of John Green's characters exhibit lolcow traits, perhaps aptly, as Green has said
Catcher in the Rye was one of his biggest influences. Also unique, though, is that a lot of his characters START as lolcows but then get better. If only reality were so kind. Here are a few of the biggest:
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Ben Starling,
Paper Towns. Ben is possibly the most overt cow Green has written, I'd say. He's a scrawny little high school band geek and professional virgin with rage, perpetually frothing at the mouth over his love life's lack of success. He's, ahem, quite the charmer: he calls women "honeybunnies" and jokes (one hops) about kidnapping a prom date. He pees blood. He insists this is due to a childhood kidney infection, the chief rumor is it's caused by chronic masturbation. He's one of the ones that improves, by the way, which happens after he does get a prom date on the rebound essentially just by being in the right place at the right time; this leads to a pretty amusing scene where he calls his best friend in the middle of the night because he's discovering women are people and
it's freaking him out.
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Chuck Parson,
Paper Towns. Chuck, a more minor character than Ben, is a roided-up lummox with maybe two brain cells at best, as I assume are most people named "Chuck Parson." Chuck is the extremely inefficient resident bully at the high school the characters go to and is basically a

to people he meets in real life. His favorite "tactic" is to twist people's arms behind their backs and only let go if they scream "I'M A FAGGOT!"

No word on if he's ever convinced someone to shove sharp pieces of plastic up their ass but I wouldn't be surprised.
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Colin Singleton,
An Abundance of Katherines. You might expect someone with the word "single" in their name to WANT WOMAN, and you'd be right. I think Colin may legitimately have some sort of disorder; it's never explicitly stated, but the combo of extremely high intelligence and extremely low social skills definitely suggests it. Colin's a high school math phenom who's perpetually unlucky in love and convinced he has nowhere to go but down. Colin wants a girlfriend, but there's a catch. For reasons too complicated to explain here, she MUST be named "Katherine." He's even come up with a mathematical equation to predict the probability of a woman named "Katherine" becoming his true and honest sweetheart. You can admire his dedication if nothing else. Thankfully he gets better too, eventually deciding to throw it all out upon, against all his predictions and calculations, falling head over heels with a girl named... Lindsey.
There's plenty more characters with at least recessive cow traits too; Green has a noted axe to grind with the "Manic Pixie Dream Girl" phenomenon and a recurring theme in his books is that both the girls in question and the guys that lust after them are kinda horrible people.