The IFS is a learning system. That means it can actually learn to pick up anything as toxic if it's reported enough times across the playerbase. This is from one of the original Riot game update posts on the IFS Reports: How do they work?
Importantly, each region owns their own community standards and we customize the system for every region to account for cultural differences. For example, in most regions, calling another player “bronze” is heavily reported, but we’ve learned that in Korea, even calling players “silver” is offensive. Youch. “Your mom” jokes vary by territory, too. In English speaking territories, “Your mom” can be silly or mean, but in Korea, “Your mom” is always deeply offensive. So keep that in mind on your next swing through Seoul.
It's just an example of something that the IFS learned in different regions. Even though the IFS isn't just a key-word filter, if the entire server decided to band together and report every instance of a particular phrase for a consistent period of time, the IFS would likely learn that the players considered it "toxic" regardless of what it was.
More recent examples of this in North America are "kys" and "c%nt." The phrase kys has always been considered toxic, but about 1-1.5 yrs ago players began to report it more consistently, both with the post-game lobby system and using tickets to Player Support. The level of response from the players, and the content of the phrase, led to it being classified as one of the most extreme levels of toxicity a player can use. The word c%nt on the other hand, has only very recently become classified as a type of hate speech for its derogatory reference of women. However, in many other parts of the world, it's considered a common slang and isn't found to be offensive. I've only been seeing players with suspensions involving this word over the last 4-6 months or so, which would mean that the system is responding to a much more recent increase in reports for its usage.