For social purposes you usually don't need the kind of anonymity that would fool a government agency, or a private investigator, or even the Googlebot. You need plausible deniability and relative obscurity.

When someone goes looking for the most embarrassing thing you ever wrote, they often find it. But we treat them the way we'd treat someone who hired a private detective: If they don't have a good reason, we conclude that they're creepy and rude.