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Yeah, ok, I guess that's good enough. It leaves off the gross-out factor part of it, but I guess that would just make it a subtrope if anything.
Of course the fact that it's so gross is precisely WHY no one would guess in a million years that was what Dr. Zoidberg had just been doing, which makes it a little bit fundamentally different, but not enough to warrant it being a different trope.
I THINK a scene in Futurama played out something like this:
The usual characters are sitting in the room with the table and Fry walks in and said "What's everyone been up to?" to which Dr. Zoidberg nervously shouted "Not drinking juice out of the dumpster, if that's what you're asking!"
Thus by denying something that was so abjectly repulsive that no one even would have ever SUSPECTED that was what he had just been doing unless they had seen him doing it, he in fact informed them that he was just doing that loathesome thing.
Is this an official trope?