I don't know where to put this actually so I guess this place is kinda fine. I have a Gambler style haircut (or Kurt Cobain ). Sometimes while chatting with random girls some will say like... "you would look better with different hair" or "I like men with short hair" or "I prefer men with dark hair"
I have no idea what to think of it. Or how to respond.

We can even broaden that comment...like when girl says..."I like tall dark men with broad shoulders and manly moustache" or "I like anorexic nerds with hipster glasses." Why are they telling me this and why should I care?

If a girl says something about your haircut then just say something back like, "Are you kidding? My hair is AMAZING" and do like a really cheesy hair flip (sarcastically of course, for the love of god don't do that seriously haha.) And if they say something about what kind of guy they like then say you like the opposite of whatever they are. If they're a tall brunette with blue eyes then say something like "Oh really cause I like short blondes with brown eyes... You know what this means...?" Girl: "What?" You: "WE'RE PERFECT FOR EACHOTHER!" Of course you can change it up to fit your style but you get the general idea. If you've just met the girl then they're probably just doing it as a shit test. Also you might actually look better with different hair. Look into that.

_________________
"Why do we feel it's necessary to yak about bullshit in order to be comfortable?"- Mia Wallace

Depending on her tone of voice, this could either be a shit test or an indicator of disinterest. Here are a few ways to react to each:

IOD: Throw an IOD back at her. "OMG you are just like my little sister (neice, cousin, etc) - cute and annoying!" *Credit Mystery...."OMG you are so sassy. When I take over the world, I am going to put you in charge of the department of sass" *Credit Mehow
Shit test: Throw an IOD such as the above OR Totally ignore it and go right into your next routine. "You know, when I was in China last month...."

The key for you is to be totally non-reactionary as if her comment didn't effect you in the slightest. Don't change your body language, facial expressions, or tone of voice. Remain happy and playful. Remember - you don't need her validation!!