I guess I should record my matches then, because toxicity was such a common thing around me in season 2-3, I couldn't believe the frequency. Most of it wasn't towards me, but when it was it usually was about my playtime or how I wasn't good with ___. I played easily over 300 matches in season 3 alone (side note: not proud of that figure, but it is what it is, I don't touch QP/arcade though). I usually played in the evening and weekends, weekends were easily the most toxic. I also noticed at the end of the season is when it reached critical mass, everyone was tilted because they weren't going to reach the rank they wanted.
This season, entirely different story thus far, but I'm not playing as much as I did season 4 (I had a ton of vacation during S3). I haven't encountered anyone that was toxic this season, this is probably around less than 30 matches total. This season has been quite the opposite than previous, have had 2 nights where everyone was being supportive of each other!