I Hate Chewing Noises

I'm struggling not to strangle my coworker who chews gum nonstop right behind me. Normally, I can just put in some headphones and listen to music to drown out the noise, but today he's being extra obnoxious, and I can still hear it through the music. Even after we told him he's being too loud, he just laughed it off and kept chewing. It's driving me to murder, and I really can't afford to do it. Someone come save me from the madness!