Mid to low Platinum/low Diamond HAS to be the MOST toxic elo hands down.
Currently plat 1 almost diamond and it's hell. People's ego are so incredibly high. Everyone thinks they're a Challenger player that never makes mistakes. I report people ALL the time for toxicity, intentional feeding, verbal abuse etc almost every game. The worst part is I barely ever get confirmation they were punished. Each time I report someone it's for a good reason. If someone goes 0/10 in lane but are clearly trying, I won't report you.
Scripting also seems to be pretty common in this elo. I've ran into 2 scripters, both Jinx's and they have yet to be banned.... (yes I am 100% sure they were scripting)
I think overall when it comes to toxicity it's just mostly an ego thing where everyone thinks they're a god at he game. Your doing something right if you've made it to Platinum, but your not all that.
Since my MMR is pretty good although I'm p1 I'm getting matched with d5 players and this one time ally Caitlyn who was d5 0 lp in s6 said "hard to teach plats the game". LMAO d5 0 lp. Exactly my point. People's head are so far in their ass.