Anything can be cool/popular, it all depends on the person involved. Agree or disagree?
Jack Nicholson was really psycho, but the unattractive sort of psycho. The sort of psycho where you want to distance yourself from said psycho.
Heath Ledger, on the other hand, was a psych o you wanted to be, to emulate.
Oops i forgot to include in the OP that these are the two takes on the same character yet they turn out completely differently.
Neither one of those was ever "the cool kid."
If you're looking for a celeb who was popular and catered to in say, high school, your most representative example would be Mark Harmon, although I don't know that the word "cool" would apply.
You're really going into intense Heath ledger-as-the-Joker melancholia tonight, aren't you, OP?
Why don't you start a couple more threads about him while you're at it?