What kind of cursing is against the rules?

The second is more likely to get you banned. The first is not at all ban-worthy.

I think cursing should not get you banned at all since, by default, you have a chat filter on as well as /all disabled. By disabling those 2 filters you're kind of asking for it. If someone's flaming you though, and trying to tilt you, it doesn't matter how many ***s you have. That should be ban-worthy, not the language itself.

It's covered in the summoner's code a bit.

Honestly, cursing is all about intent and purpose. Derogatory terms, racial/homophobic or otherwise, have absolutely no purpose in this game whatsoever.

A quick curse at the situation is fine ("Shit, they're at baron!"), and the occasional quip ("Man, they really f*ked my gank up there!") is totally fine. Cursing at people ("f*k you!" "stfu" "go to hell, b*") with malicious intent is not okay. Generally you don't want to call your friends the n-word even as a joke, but saying something silly like "What's up my bitches" when you're playing all for one Nasus is something else entirely.

The only "curses" you get banned for are racial, homophobic slurs and the likes. Otherwise you can say all the evil words you have memorized, as long as none of them are directed at any person that can hear them. Kinda like when you stub your pinky, screaming every swear word in existence at the table is completely fine, acceptable and relatable.

Avoid racial slurs and homophobic terms, other than that you can cuss as much as you want as long not toward anyone, but if your teammates asking you to stop, please stop. I avoid chat 99% of my games, cause this is the internet and you'll never know when you rubs someone the wrong way. http://www.auplod.com/u/uopadl6d63e.png