A paper from computer scientists from the University of Washington, Carnegie Mellon University, and the Allen Institute for Artificial Intelligence, found that machines were more likely to flag tweets from black people than white people as offensive:

It all boils down to the subtle differences in language. African-American English (AAE), often spoken in urban communities, is peppered with racial slang and profanities.

But even if they contain what appear to be offensive words, the message itself often isn’t abusive. For example, the tweet “I saw him yesterday” is scored as 6 per cent toxic, but it suddenly skyrockets to 95 per cent for the comment “I saw his ass yesterday”. The word ass may be crude, but when used in that context it’s not aggressive at all.. . [eutimes.net]