[Tao3300]

There are probably some types of glass that work better for it than others. I only looked at two of the videos and they were both a guy in Brazil eating a very particular type of drinking glass, which has me thinking these guys aren't just wolfing down pint glasses in UK pubs or something -- this is one particular glass that they 'can' pull this off with.

It would take a bit of finesse and the right mouth for it, but as long as you didn't surprise your soft bits with sudden movement across or into a sharp piece... maybe?

[kadoban]

Maybe. It doesn't sound completely physically impossible, but it's like...even if you could do it, why wouldn't you just use sugar glass or some other trick? Infinitely safer and more fun for the same result.