It's not so much claiming to be an oldfag or a newfag - though actually having experience with the website is nice.
It's more about being a smart poster (whether you're trolling or being serious, aka doing it wrong). A lot of people just call others newfags because they think 4chan is their secret club nobody should know about, clinging on to old memes as if they're some sort of secret currency. Then *they* look like the tools.
And while I think idiots should go away, I'm more than willing to accept new people if they're not fucking stupid.