If the NSA spots half a dozen people on Crypto-Reddit's /r/boston who claim to be from San Francisco, New York, Seattle, Chicago, rural Tennessee, and Miami respectively, then it knows it has probably found six actual Bostonians.

Individuals are in many ways an expression of our context. To remove all information leakage that would tell what our context is or, more simply, who we are, you basically have to remove the person entirely. Even 4chan-grade anonymity won't cut it, since writing style and narrative threading can be used to extract some sense of pseudonymity from even a /b/ thread.