[kemayo]

Given that you don't mention seeing blood, this was almost certainly just someone playing a prank by eating sugar glass. It's slightly thickened melted sugar that you've let set into a thin pane. Looks just like glass, but it's really rock candy and so you can break it up and chew it.

https://www.inthekitchenwithmatt.com/edible-sugar-glass

[techload]

No. It was a glass from the bar, and a thick walled one. There was no blood. He did this thing several times. He did not die, as I met him several years after. It is a glass like this one, common in Brazilian bars:

https://youtu.be/xwrn2h8iAdw

[augusto-moura]

You probably mean a Copo Americano (American Glass) [1]. Also note, that eating glass is also a common magic trick, David Blaine is famous for doing it [2], I'm not sure how real is the glass though

[1]: https://en.wikipedia.org/wiki/Copo_americano

[2]: https://youtu.be/MewROa1EU_o?si=Vysz1UfyWV44AEd_&t=83

[kadoban]

I'd still think it's more likely it was a magic trick or scam.

[techload]

There are a lot of people who do this, amazing and unbelievable as it may seem.

https://youtu.be/WUuMybRysjE

https://youtu.be/O8ifaTHbMTo

https://youtu.be/JFnGsGnlkAI

https://www.youtube.com/shorts/5OdkhtMEqMo?feature=share

[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.

[kemayo]

With only minor collusion with the bartender, you can just arrange to be given a glass made of sugar-glass.

https://www.makeyourownmolds.com/how-to-sugar-glass-mold/