I've occasionally challenged people about minor things - things that I don't think they're doing on purpose - and they're usually apologetic and accommodate. Rarely, I'll use a polite CM voice to encourage someone to do something they don't necessarily want to do, which usually works.
Having said that, during a Haunted Mansion Holiday visit last fall:
We're in the stretch room, and there's a college-age woman wearing light-up Zero ears. They're bright. Since they're on her head, I'm assuming she doesn't realize that she's blinding everybody - she may not even know that they're turned on. I try to get her attention, but she doesn't move. I assume she can't hear me, so I snap my finger behind her head. That works. I gently point out the lights on her head, and ask if she might be willing to turn them off. I'm assuming she'll give me an, "OMG, I'm so sorry, I forgot I had them on" reaction.
Nope. Her reaction, hostilely: "I'm not going to do anything for someone who snaps at me." I try to apologize and explain, but she's not having it.
We get out of the room and into the hallway - I move away from her. (A couple of families told me they were thinking the same thing and gave me credit for trying.) I eventually feel somebody grab me by the shoulder. It's apparently the woman's boyfriend. He seems nice enough - nothing especially hostile - but he challenges me as to what I said to her that offended her. I explain in full that I meant no harm, but that the lights on her ears are ruining the experience for everyone around her - it's a dark ride, after all. He seems to get it and goes back to her.
I get on the ride, and I notice in the mirrors that they're like five buggies behind me. She's got a pout on her face - and still has the ears turned on - basically ruining the ride for her boyfriend and the buggies around her.