Aren't we all adults?

I'm not really new to MOBAS, I absolutely love Dota 2 (1200 hours) and smite (100ish). And I've been playing and enjoying league now for close to two months. I understand how most of the communities are in terms of rudeness (The elitists etc etc). But it seems as though most of the league community's tolerance for even the slightest negativity is a bit much. Let me explain.

I just recently had a game where our Jungler was playing a new hero to him. Our top lane riven was being slammed by a zed and asked for a gank. The jungler told him he wouldn't be much help since he's playing a new hero. The top laner, and myself asked him why he isn't practicing on bots instead of a real match. He replied saying he'd rather play against people. Low and behold the top laner died again and DCd because of the lack of ganks. I pointed out that's usually the reason why you shouldn't practice in a pub match. Top came mid (My lane) and frustratingly I said gg. To which our support screamed TOXIC and threatened to report. Being honest with everyone here I told him he's being acting like a baby. To which his reply was now that I called him a baby I'm eligible to be banned.

I understand that league's situation with toxic players is way worse than Dota 2's. But come on. As the title states. We're all adults. I can understand if someone spammed racial slurs or homophobic curses. I understand if someone is trolling, I get most of it. But where does this mentality stem from? That anything said if even a tiny bit negative is worthy of being reported.

And I know the first response to this is going to be Negative attitude is a on the list of report logs so it's totally allowed. But I assume that's meant for the teammate who just doesn't shut up about how your team will be unable to win.

I don't know. I guess I'm used to no one caring when someone curses or says something rude on other MOBAS.