One of my verrrry minor bugbears is people who show up to 3k or 5k fun runs wearing gear promoting events well above the event's level.
Like "okay dude, that's a nice Antarctica Marathon t-shirt but it's not going to make you look cooler in the Buttfucknowheresville Gala 5k", or "settle down Mrs London Marathon windbreaker over your Kona Ironman tech tee, you're going up against someone with a cotton T-shirt from Asda and thick shorts that are going to build up enough charge to power a small African country".
Big respect to the effort they put in to earn the gear, but who are they honestly trying to impress?