I work with a popper/loud chewer. I put headphones on with music and could STILL hear him. So I very politely asked him if he would not pop anymore, or chew open mouthed, because it was quite distracting in a nails-on-a-blackboard kind of way, and that I DID try to block him out with the headphones but it didn't work, so could he please be more mindful. He has improved (not stopped totally) but what's more annoying now is that he's a bit snarky and acts like a victim and brings up my request to elicit sympathy, like I'm a mean person. But I have called him out on that, too, by using humor. So it hasn't escalated and things are okay. But it irks me that he tries to make me out to be a bad guy when he's the rude one! He also keeps 2 liter bottles of soda under his desk to refill his drink cup, and eats snacks out of loud plastic bags that crinkle and make a lot of noise, like pretzels and chips. That bugs me too, more for sanitary reasons than the noise. But I'm not complaining about that. I pick my battles, and the gum popping is way worse to me, so that's what I keep focusing on and trying to stop.