As a runner I have to stand up for this demographic a bit
Nobody could think runners are cocky who's really talked to any. They're people with realistic goals that work hard to do something which is often challenging. Getting up to go running most days certainly isn't easy and nobody would do it just to be able to brag. That would be way too much work. Most of the legit ones also weight train to get their endurance up and aren't the muscle-less scrawny guys that are stereotyped. I don't even see the reason why runners would be cocky. It's not like we're amazing at any particular skill. We're just in good shape and know how to get up early in the morning or late in the evening and do work to maintain healthiness. Everybody should try it sometime.