Never happened to me but I’ve seen many who should have been denied boarding.
Most of my flying is for leisure, on charter airlines where the standard of dress is more relaxed. Even on scheduled flights, the fashion police should still be summoned. Guys, when you’ve lost the firmness of youth, leaving your shirt completely unbuttoned or wearing a vest/singlet may look great around the pool, but not on your flight home. Likewise my fellow females, wear loose fitting trousers instead of lycra crops that are two sizes too small!
Seriously, UA should have better communicated their dress code for “perk” ticket passengers so that this issue was resolved before they arrived at the airport. Would be interested to see a picture of the offending leggings…….