It's fine to hold yourself to a higher standard, but just because you do, doesn't mean everyone else will. Anyways, if you really do have high self-esteem, you won't let something said over the internet rattle you. What I'm trying to say is that yes, its not nice to insult someone's skill over the internet, but it's not offensive either. There's a line you have to cross to be offensive and it usually involves insulting aspects or qualities of a person that are uncontrollable or can't be changed, ie: race, intelligence, gender, religion, nationality. Insulting a person's skill is something that not only can be improved but is also subject to different interpretation, like I could say someone is trash at a champion, but someone in bronze elo might consider the player good in comparison. Basically, you shouldn't be offended by someone insulting a trait that you acquired on your own and can change at your own volition. It's still bad manners and not nice, but just like real life some people are nice and some people are not, and the mean people are not always going to suffer repercussions for their attitude even if you think they deserve it.