Why are people loading in cussing and being jerks? (Its a trap)

I just don't get it, I literally had 2 people load into champion select pissed as all hell and it only got worse as the game went on. The support bard started on his ADC right away calling him stupid for wanting to invade. Next the GP starts trash talking me cuz I happened to be walking behind his turret when he got blown up by a mid-lane Kalista (Kalista and Cass lane swapped). But just negative harassment form the word go.

I figured it out finally after MF cussed at them in the post game screen. They were trying to bait us into cursing at them so the report system would get us. This is an underhanded truly cowardly thing to do and I don't know what to do about it. I can mute them, I can tell my team to mute them, but what about the next poor team? These guys are wrecking games and they are being really creative in there attacks on other players so they cant be reported back as easily.