It's very common. "I don't care about looking cool" very often means "I care about NOT looking cool", or "I care about not looking like a n00b".
There's also a big difference between "I don't care how I look" and "I want to look like I don't care."
Typically, the more vocal someone is about being in the former group... the more likely they are in the latter.
If you truly didn't care how you looked it would never occur to you comment on how you looked one way or the other... because you don't care. If you didn't care, you wouldn't spend a lot of time defending how much you don't care, telling everyone you "don't give a ****" and and making negative comments about people who do happen to care about how they look.
In the Audi forums there's a whole subset of people who remove all the badging, crome, etc from their cars, change out the wheels, smoke the sidelights, etc - often spending tens of thousands of dollars in the process - claiming they do this because they "care more about function than how it looks."