We can solve this once and for all:
kook
/ko͞ok/
nouninformal•North American
noun: kook; plural noun: kooks
a crazy or eccentric person.
Origin
1960s: probably from cuckoo.
He markets himself as eccentric and doing things like wearing a helmet even if it was not widely socially accepted. So yes, he is a kook and we don't have to be derogatory to say as much, if it makes us feel better.
Skateboarders as a whole are kooks to the rest of society, so it is perhaps all relative.