You've opened a can of worms here. I'm not sure people look at Mendy and think because he's black that he's a troublemaker of some sorts.It's not bollocks, it's something else entirely .
The successful, didnt-know-his-place Mario Ballotelli used to get similar vitriol, as does Raheem Sterling whenever he misplaces a pass etc.
KDB never seems to get the same grief .And nor should he.
However, in the interest of balance, there is a thing called unconscious bias. Many psychologists believe most people have somewhat innate and minor racist behaviours/thoughts due to such unconscious biases that are imprinted. It's definitely out there, the media treatment of Sterling (and others) has some elements of this. To suggest users on here though have any trace of that is dangerous and as you can already imagine, offensive (to some).
I do think this is a serious claim however, especially if there's any remote hint of truth.