Riot puts a lot of emphasis on not dictating the rules for the community.
The players passively decide what type of behavior they deem acceptable through honoring or reporting players who show certain behavior. 
It is almost impossible to post a list of rules that make it certain what behavior is punished because language and behavior standards are constantly evolving. 
One of Riot’s goals regarding Player Behavior standards is to adapt them to real-life standards. What isn’t acceptable to say in real-life, shouldn’t be acceptable on the internet either, according to Riot. 
When the Instant Feedback System was launched, a lot of data was taken from the Old Tribunal to “teach” the system what the community previously recognized as offensive.
Riot has also gathered information from social media. 
Due to cultural differences, each region decides what type of behavior they tolerate individually, which is why the system acts different in all regions.
“Your mom” for example can be a silly or mean phrase in NA, while it is always considered highly offensive in Korea. 
Riot is unsure what they will do in case players create a standard they don’t agree with. This has never been the case in the past, since the community generally does a good job judging behavior. 
Explicit language is not inherently punishable, as long as it is kept to a moderate level and not directed at any players. 
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389 https://ask.fm/RiotLyte/answers/130717609922 ; Page 283
423 https://ask.fm/RiotLyte/answers/130891598530 ; Page 243