This was a crazy one! In short, there was a race condition. Reveal the spoiler for a more detailed explanation, as it contains the trigger for the hat:
There was a race condition in the variable that stored the synonym for discussion tags across website, and they were all defaulting to "discussion" as opposed to the localized version (big thanks to Roberta Arcoverde for figuring this one out!).
The race condition has been fixed. Going forward folks should now be able to attain the hat by performing the trigger. It is not possible to award hats going backwards to people that already did it though, since the actual detector wasn't being rendered to the page (sorry about that :( )