I feel obliged to point out the this Doctor is bitchy and snarky to everyone. The fact that it's being over-examined in relation to a black character just shows how sensitive people are to the possibility, of prejudice rather than the actuality of whether it's there.
In the last few episodes, from brief memory (I've only seen each of them once after all ;P) he's belittled Clara (his best friend, I might add) as old, fat, and unattractive in entirely jocular manner.
He's picked on other soldiers (White. Female), and has in turn been highly resistant to the suggestion that he himself is a hero, fighter, soldier (or Dalek ;P) when that is pointed out to him. He was also dismissive and brusque towards Psi last week (and actually quite happy that he's an augmented human, seemingly finding them a better prospect than a 'normal' human) enough so that Psi quite openly told Clara she shouldn't trust him.
He is that abrasive... to everyone. He makes absolutely no secret that he views soldiers (particularly ones that just obey orders) as a very bad thing. He's mean to everyone. He makes jokes at other peoples expense, and picks on everyone quite equally. And I suspect he appreciates the few people that actually stand up to him as the strong people they are that are worthy of respect, namely Clara. (Edit: And now Danny Pink as well, I suspect)
Why exactly do people feel the need to fixate on just one of those victims and pick that out as a special, rather than seeing that it is just one of many examples treated equally badly?
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