Unpopular opinion but yelling c'mon after your opponent makes an error shouldn't matter. If you don't want your opponent to do that, then don't make errors, and if it actually bothers you, then that's on you, not your opponent. I guess if people find that annoying that's fine, but I really don't think it's poor sportsmanship, at worst it's just a tactic, but in Gauff's case she's clearly just trying to get herself pumped up in big moments. It's not a Collins roar-in-the-opponents'-face come-on, which is clearly worse sportsmanship (but still doesn't bug me, frankly).