A harsh reality of working out in a health club is that it's not yours. You have to share the space and equipment with several hundred other people who are likely equally perturbed that they have to share it with you. It's a concession we make to have access to all those fancy machines we can't afford to put in our homes. So we make the best of it, abandon our OCD and antisocial tendencies, wipe that last guy's sweat from the treadmill, smile politely at the infuriatingly cheery front desk staff, and go about our business.
Most of us, that is. There always seem to be a few regulars who eschew the spirit of cooperation, never letting the rest of us forget that 1) they're there, and 2) they'd prefer us not to be. These types are either desperate for attention or hellbent on taking out their frustrations on everyone near them---sometimes both. This is often expressed with loud, angry grunting, giving you the evil eye if you dare ask to work in a set, and being obnoxious just because they can.
There's a guy at my gym---I'd put him in his early 50s---who insists on popping his gum as loudly as possible whenever someone approaches the elliptical machine next to his. It's like he's firing a warning shot: get too close and you're gonna pay! He reminds me of a member at the last club where I worked who used to let out the occasional huge belch. He didn't care if anyone was nearby; if anything he did it because they were nearby.
Whether the bad behavior is claiming a bench with a gym bag or refusing to wipe sweat off the equipment, the common thread here seems to be a sense of entitlement. I was here first; I'm in here every day, I can do what I want; I'm bigger than you. It's like the driver on a crowded freeway who won't allow entering traffic to merge. We share the road; similarly, we have to share the health club. At least until we're all so rich that we can afford home gyms.