Literally would crunch ice from a big metal cup ALL DAY LONG (walk to the soda fountain in the break room and refill with ice every hour).

I encountered two people like this in my life. It would make me physically ill, like an allergy, but no one else around us complained so I tried to get over it and ended up just working in a lab.

I'm old enough now were it to happen again I'd flood every channel with complaints until we arrived at a compromise, but I was younger then.

> It would make me physically ill

This is a classic instance of misophonia. Certain sounds, especially sounds related to eating, generate disproportionate and irrational reactions, often (internally) physical. Anything from fear to disgust to anger, with the accompanying bodily state.

Some people love to literally crush ice in their mouth.

I cannot stand it. On top of just being an annoying sound, it makes me think about / feel pain, because it sounds like it really hurts.

I love it, but it does tend to freak out at least a few people. They claim I'll crack my teeth or something, but that's probably just a cover for how it makes them feel.

Yes, it could be bad for my teeth, but that's likely not why they're telling me about it. It bothers them more than it concerns them, or they'd stop telling me about it after a few times.

Ice chewing is a 'possible' symptom of anemia : https://www.mayoclinic.org/diseases-conditions/iron-deficien...

I sat next to a literal ice-chewer.