Well, Riot DOES have a specific list. I don't think it is inclusive, but it is pretty comprehensive.
I would like to give special attention to section V, part E.
It reads (actual text) "Transmitting or communicating any content which, in the sole and exclusive discretion of Riot Games, is deemed offensive".
There is NO clause that says "unless someone did it to you first". So, if we want to debate whether section V part E of the EULA is well written, that's one thing. But beyond that, the system is working exactly as intended in upholding that part of the agreement.
From End User License Agreement http://na.leagueoflegends.com/legal/eula
III. Additional Agreements
You hereby agree you will not
C) Modify game files
D) Sell content owned by Riot
E) Use scripts
V. Code of Conduct
The following are examples of behavior that warrant disciplinary measures:
A) Impersonating Riot
B) Posting personal identifying information about yourself or others
C) Harassing, stalking, or threatening others
D) Screwing around with Riot's intellectual property
E) Communicating content deemed offensive by Riot (including, but not limited to, language that is unlawful, harmful, threatening, abusive, harassing, defamatory, vulgar, obscene, sexually explicit, or racially, ethnically, or otherwise objectionable)
F) Sending viruses and the like
G) Spamming
H) Exploiting an undocumented and/or unintended aspect of the game
I) Defrauding other users of the game
J) Attempting to access closed parts of the game
K) Leaving games
L) Picking a summoner name that Riot objects to.
I mean, this stuff isn't that difficult to find, and considering the greatest lie ever spoken in the world (I hereby acknowledge that I have read and agree to these terms and conditions), you cannot pretend it hasn't been presented to you in one fashion or another.