It's always been this way but recently there's a spike in this sort of behavior. Why do people bring up rank in a casual setting as a way to argue? For example, let's say we have a silver adc and gold support (there's not even that much of a rank difference and yet they do this). Silver adc plays poorly, gold support flames, adc argues back, support looks adc up and says "you're silver trash, you don't know anything" (ok? like a gold 4 support is going to know much more than a silver 3 adc)
It even happens in the reverse. Let's say we have a diamond top and gold mid. Diamond top dies in lane a couple of times, mid looks up diamond player and goes "jesus you're diamond why are you so fking bad? boosted? ebay?"
Relax people. These are NORMAL games.