The grossest thing I can think of is if you don’t drink an Irish Car Bomb fast enough, and it curdles.
Although last week I ordered this special bottle-conditioned beer (meaning there are still active/living yeast cells inside). One of the bottles came in missing a cork, so it was basically an open science experiment. It had turned into this thick and goopy tan… stuff that smelled like a nasty gym locker full of sweaty socks. Accidentally catching a whiff of that made me throw up in my mouth a little. I had to dump it down the sink and the lumps were like, glug, glug, glug. I LOVE trappist ales, but goddamn. It’s going to be a while before I can drink one again.