Why not crowdsource it?
Here's a possible idea:
Encourage people to vote for the 'tag' on a question (up or down, for reasons you'll see in a minute)
If the votes for a particular tag ('fun', gtky, etc.) exceed a certain threshold (10? 15?), then all of the answers and the question are 'cut off' from badges.
You'd obviously need to allow your 10K users (grin) to vote to put badges in the 'this doesn't count towards badges' pile.
Possible issues with this:
Once people learned that their precious badges could be lost with people voting on tags, they may not vote. So the only badges that ought to be lost are the gold badges. The rest are relatively trivial to get.
Secondly, you'd have to reward people voting on the tagging system for questions. Voting on tags would also allow people who cannot yet vote to determine what tags may be 'innappropriate' for a question, and would get out of the tag wars that we encounter from time to time (though it mostly happens because of that damned taxonomist badge, which already suffers from too much human moderation and not enough programming moderation).