A handful of times...
First time i remember seeing one was in school. A girl in the grade above came in wearing a cervical headgear, and then proceeded to wear it many days at school. She was a cool girl, very popular, so at first it was shocking that she would wear it to school, by the 2nd or 3rd time, everyone got used to it. She was very confident wearing it - just pretended it was no big deal.
At summer camp when I was probably 10, one of my bunk mates had a reverse pull mask. He was very studious to never put it on until after the lights were out, but every morning he'd wake up with it on (and then quickly stash it). I think he was more embarrassed than he needed to be - many of the kids in the cabin had braces/retainers etc..
In high school I remember once seeing a younger girl (9th grade) wearing one (again, cervical) in study hall. She was clearly embarrassed to be seen wearing it when my class came into the study room and quickly removed it.
More recently, I saw a teenage girl in the Las Vegas airport wearing a high-pull headgear getting off a plane. I think this was still the only time I've seen a high-pull 'in the wild' so the memory definitely stuck with me.
When I had braces in 2012/2013, there was one time at the ortho office where a young boy was getting fitted for a headgear. I could only hear the discussion, but he was clearly not loving the idea, and his mother was trying to reassure him that it would only be at night etc etc. He walked out with a standard cervical headgear / boring blue strap.
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