This actually comes up a lot more than you'd think. People seem to want a very specific list of "all the things I can't say in game so I never get punished." Making a specific list would actually be more effort than its worth. Having a generalized "harassment and insults will not be tolerated" is actually healthier for the game as what people consider "harassment" changes over time; "kys" was not a popular phrase when League launched. Also, people who tend to skirt the rules and get away with it would have a much easier time getting around a specific list. For example, "the list says you can't say 'you're bad' but I said 'your bad' so I'm not breaking any rules since they are two different words."
Can you find a way to be offended at almost anything? Sure, of course you can. If someone talks about soda, I can say I'm offended that you'd talk about soda so openly when I'm clearly on a diet. But, that wouldn't fly, you wouldn't get punished for that. If "soda" became keyword for "SO Damn Annoying" and people started using that to harass others, then sure, at that point it'd be considered harassment.
When looking at the question as a whole however, context is more important than what you say. If I'm running from an enemy and manage to Flash over the thick wall in top lane, my teammate might say "nice Flash" as a way to complement my years of practice. If I fail the flash and then subsequently die, they might say "nice Flash" sarcastically, as a way to mock or otherwise harass me. In both scenarios, everything is the same, but I've failed in one and succeeded in another. Because you can give backhanded compliments and use that as a form of harassment, do you think that all compliments should be banned from chat? Do you think that people should be allowed to remark sarcastically and never get punished? Absolutes don't really work well when it comes to rules. Extenuating circumstances exist for every rule that's ever been thought of.
So here we've come to why Riot has the policy they do when it comes to harassment. It would be too exhausting to keep a list of every insult hurled someone's way. Some of those phrases may even be completely innocent, but because they are used to harass, they're banned. Even if you did, and banned those phrases, people would still find a way to harass others. Back when it was possible to get infinite chat restrictions, those it applied to (the trolls that simply wouldn't quit) found other ways to be a nuisance. Hiding in a bush all game, intentionally feeding, etc. While restricting their speech did have the intended result - they can't talk anymore - it brought up other unintended problems.
I understand your plight, you want to make sure you won't be banned because someone was a little more sensitive than you anticipated. If your intent truly is not to harass others, then you have nothing to worry about. The general rule of thumb is, don't talk about politics, sex, or religion around those you're not familiar with. I've lived by this since my grandfather taught me when I was a boy and it's worked well so far.
Let me know if I can be of more help.
