I haven't needed this yet today, but I'm sure it's coming.

"MLK had a dream where people would be judged by the content of their character and not the color of their skin, therefore, racism is dead and has been for 60 years" - some chud just before or after saying something horrifically racist

Why was it only a dream mf? TELL ME WHY IT WAS ONLY A DREAM!?
- It was Clippy's fault. Get'em!

It does seem true though that MLK would have been a vehement opponent of racism towards white people. His words and teachings would not support the idea that "black people can't be racist" and similar modern catechisms. These are harmful concepts that only further entrench white supremacy as people living in fear won't be open to higher minded insight.

I think that's a saying because racism is only harmful when people in positions of power act on their racism and black people traditionally don't have power in this country. If a black judge is only prosecuting white people or anyone else that isn't black, guilty or innocent, that's a case of a black racist. But that situation is way more likely if the judge is white and only prosecuting minorities
As brief overview:
I generally only hear people in common conversation complaining that someone told them once that they heard someone say black people can't be racist. I don't think I've seen anyone in the wild claim it with a straight face - because many people use racism and bigotry interchangeably, and it's quite plain that anyone can be a bigot. However:
Racism by sociological definition is something that only the group in power can engage in (paraphrasing) so your problem, like most people who bring this up, is probably:
You heard from someone that someone else said "black people can't be racist" one time, but have probably never actually been told "black people can't be racist." (Which is sort of multiple layers of irony, because if you define the word correctly, they can't, at least generally not in the US.)
and/or
You are using racism and bigotry as synonyms. Anyone can be a bigot, racially prejudiced, etc. Black folks can absolutely be bigoted and racially prejudiced towards others, just like anyone else can.
Here's a snippet of a definition from an into to sociology:
Racism is a stronger type of prejudice and discrimination used to justify inequalities against individuals by maintaining that one racial category is somehow superior or inferior to others; it is a set of practices used by a racial dominant group to maximize advantages for itself by disadvantaging racial minority groups.
The text goes on to say this doesn't preclude racial minorities from being prejudiced, bigots, etc.
And finally, and really this was all that truly needed to be said: In my experience, most of what people complain about online as "racism against white people" turns out to be nothing of the sort, and I'm personally doubtful MLK would have had a sympathetic ear for the common examples I see, either.
Edit: Forgot the link.
Edit again: Still forgot the link
https://openstax.org/books/introduction-sociology-3e/pages/11-3-prejudice-discrimination-and-racism
Edit - so many edits to be sure I'm saying what I mean to.
- Here's the ACTUAL definition of racism:
  "prejudice, discrimination, or antagonism by an individual, community, or institution against a person or people on the basis of their membership in a particular racial or ethnic group, typically one that is a minority or marginalized."
  Please get out of here with that "Only people in the dominant group can be racist" mumbo jumbo. That may be the more typical case, but it's not the only one. You (and the author of the sociology textbook you quoted) are EXACTLY the type of people OP was talking about, and that's why you're being downvoted here.

I find a weird coincidence between their choice of a mascot and the Paperclip operation to retrieve scientist from nazi Germany. Yes, it's a basic office supply. But yes, american users consulted it with their problems just like these scientist. There's a little gist of an irony in that, albeit probably not intentional.

What did you take before typing that?
- 40% vodka?

Considering what Microsoft is, expect clippy to support a white nationalist narrative.

I would love to read your reasoning.
- Just look at that little fucker’s face
- Microsoft is headquartered in Seattle, a known Nazi stronghold. Obviously.