I've seen tweets that are nothing but innocuous gifs get marked as offensive. Several examples in there are people responding to k-pop Tweets with identical statements (e.g. "I like so and so the best") and one will be marked offensive and the other won't. Sometimes almost identical tweets by the same person are considered offensive or not.
However sophisticated Twitter's algorithm is, and whatever data and behavior it takes into account, my contention is that it isn't very good and produces poor results. If people can't tell the difference between offensive and inoffensive tweets any better than chance - then what is Twitter really doing?
the use of negative words suck as 'sucks' or 'terrible'
account-wide penalty. Some accounts will have all their tweets marked as offensive no matter where they post or what they post
some accounts,especially well-known verified accounts, will have a much lower threshold for tweets to be marked as offensive, regardless of language.
tweets that contain images, videos, and or links at much higher risk of being marked as offensive
tweets from new accounts and or accounts with few followers more likely to be marked as offensive
tweets with links from certain domains and or host IPs will be marked as offensive
IP of the twitter account user and or where it was created
a tweet with preview text from a link that contains certain content will be market as offensive