'Big Bang Theory' because it doesn't have a black character. A trait it shares with numerous other successful sit-coms. Not racist in any sense beyond that, save perhaps for one bit of dialog:
Sheldon: Yes, enjoy your japes, gentlemen. You think you’ve poked fun at a milquetoast academic. Well, you’ve forgotten one thing. I am also a son of the Lone Star state. I’m Texas through and through. And we know how to settle scores down there. If you doubt me, ask Mexico.
The joke is interesting. Did the writing staff (and television shows tend to have large staffs, 'The Colbert Report' has 22 full-time writers) find humor in the idea of a geek character being a bit chauvanistic? Or was it a subtle jab at the sort of chili peppers one has to deal with in L.A.?
If BBT had a black character, or a Mexican character, imagine the dilemma. The obligatory stale jokes, 'Oh, so you saying a black man can't be a scientist? Oh, sho' nuff boss, I'll calibrate dat particle accelerator right aways boss suh!'
Would the writers be able to poke fun at NAM characters in the same way they do with Raj or Sheldon? I doubt it. You can only go so far, seeing as how it's 'too soon', and it's always 'too soon'.
If you can't be kidded then you're not a part of the family. And sit-coms require family.