If you troll/say gg ez(spamming it and using other forms of it and the stupid "??" after a bad play/intentional feed/willingly click the exit game button/or just flat out afk and stay in game but move around.
These types of people need to be punished thoroughly, however using swear words and having a good time talking like immature brats jokingly with one another and getting banned for such small things don't need punished. Being punished for just joking around with the enemy team via vulgar chat socialization as well as team mates and losing the ability to earn end of season rewards/hextech loot only makes the game more toxic, it puts people on tilt and they hate it, everyone hates it because it's just a garbage way of going about punishment, it isn't fair for anyone. If someone admits to being a smurf via chat logs, they should be unable to earn full IP(Earn Half IP/Unable to buy their champion with RP but can buy hextech loot at a chance to gain their main champion). This would make it fair for new players coming into the game cause it would cut down on smurfs, and make players have a fun experience instead of dealing with Ekkos/Yasuos running around steamrolling everyone.