This is deeply un-funny to me. Here are three reasons why.
1. It mocks a real, important campaign. This one, to be exact. USAmericans have a real problem with creating offensive Halloween costumes. Hello? Blackface is not ok. Sticking a feather in your hair, dashing on some red paint, and saying you're an "Indian princess" or, for fuck's sake, a "Poca-hottie" is NOT OK. People of color are PEOPLE, not costumes.
2. It fat-shames. Stereotypes abound regarding nerds as fat, pasty basement-dwellers completely sans social skills. This, like any stereotype about a group, is often inaccurate, and is yet another arm of our society's obsession with policing others' bodies. Think body shame doesn't touch nerd-dom? We're not immune.
3. The Doctor would never do this. On a totally petty, fannish, basic level--THE DOCTOR WOULD NOT DO THIS. This is not the MO of a thousands-year-old being who's literally seen everything. He's never met an unimportant person. He's a dick in many ways, but this ain't his brand.
Call me a humorless feminist, I do not care. There are millions of Halloween costumes in the world without needing to dip into abuse of cultures that have already been destroyed, ignored, bastardized, and stolen from. It's so easy to not be an racist asshole. All it takes is the tiniest bit of thought and absolutely no effort.