Mute players -> refusing to communicate -> banned Flame -> abusive -> banned Any curse word -> whatever reason you want to put -> banned Not receiving end-of-season rewards you earned by playing the game because you said a bad word and got banned once -> priceless
It's not the words you use, but how you use them.
If you say something like "I fucked up," you won't get punished, this is normal speech and not inherently toxic. However, if you say, "You fucking suck" the intent behind that is toxic towards another person, thus punishable.
Here is Lyte talking about this in an older post:
This is a pretty nuanced topic. There really isn't a list of phrases or words somewhere that dictates what's good or bad, and usually it comes down to the attitude and the harm you're inflicting on other players.
To add to the other comment:
Mute players -> refusing to communicate -> banned
Wrong. Riot's stance has always been that pinging is a sufficient means of communication. It doesn't require you to type in chat at all. If it did, I'd have been banned years ago, because I rarely ever say anything in chat all game (frankly, this is a great way to avoid bans).
