Thanks for clarifying "hair shirt". I'd seen you mention it at least 3 times previously in comments, and was trying to unpack it without doing a search. Thoughts such as "they're quite fond of stylish hair and t-shirts?" and "they like t-shirts with hair designs?". I think my worst take was "they fetishize wearing someone else's chest hair, like a shirt?"

Popped onto DDG just now, and the explains right there. Also "cilice" within the first few links.