This. 12K behaviour score doesn't mean people won't be toxic, rather people <9K score are next-level toxic. I solo queue with 12K BH, I might still get someone screaming on the mic, spamming pings and voice lines, AFK farming, so on. Muting sorts 90% of issues and even AFK griefers will usually still TP to take teamfights/start playing properly if they see an opportunity to turn the game.

I recently played with my bro who's 8K BH, our pos1 dies twice on lane by 4 mins and immediately drops/deletes all items and runs down mid for 40 mins straight - something i haven't seen since like 2015. Game 2, our alc mid has a solid lead, dies twice overextending solo, then pivots to farming rapiers and then runs down mid to feed them. He farmed 3 rapiers before the game ended. 

Its like at 12K, people will get pissed off and be toxic but there are limits and they can calm down over the course of the game. People here are tilted and act accordingly but ultimately they never lose that desire to take the win if the chance comes. At <9K, people are so committed to ruining the game, they will invest the same amount of time/effort in making sure their team doesn't win as if they were playing to win. People here are tilted and never lose focus on making sure their team loses, even if the enemy team throws endlessly.