The apocalypse is nigh -- yesterday, a "Jersey Shore" cast member gave a guest lecture at an Ivy League school ...
It actually makes a lot more sense when you know the full story -- sources tell TMZ, Vinny Guadagnino was invited to speak in a Columbia sociology class on "deviance" ... a subject on which Vinny is a recognized expert.
Vin spent a lot of time talking about being bullied growing up. It went really well -- we're told students even applauded at the end -- but crap got real when Vinny opened the floor up for questions.
We're told one observer bluntly asked, "What gives you, as a cast member of 'Jersey Shore,' the right to interrupt this class and then lecture us on setting a good example?"
Vinny -- who wasn't big on speech and debate in high school -- was predictably stumped.