Over the countless times I played through my Leaf Green version, I never grabbed the opportunity to name my rival something like asshole or the likes. I believe I named him Gary most of the time, as that was the name I'd always identified him with, so I didn't really see much reason to name him anything else I guess. The funny thing is that he was the only rival this ever applied to (aside from the R/B rival since they're basically the same), as in most of the other games, I'd usually find some kind of condescending name to call my rival, but for the Kanto rival, it was just mostly always Gary, which I guess is just from how the anime has influenced me.