Right, so just that I'm clear, what is a privilege check, and why was what bt was doing calling one wrong?
Saying "check your privilege", outside of a humorous or trolling or drama-baiting context, means "your perspective as a X might mean that you're unaware that other groups struggle with issues like Y." [Or of how much, or the nature of Y, or whatever.] It originates as a phrase meant to be used between people who already know what is meant by "privilege". (Otherwise, we'd just use that phrase.) Essentially, it's a shorthand. I've used it myself, though of course I wouldn't use that phrase outside of contexts where people understand what I mean by it. You know. Like on this website. (Though I am perfectly willing to discuss the concept, of course.)
When the phrase "check your privilege" is used in other contexts besides the one I just mentioned, it is almost exclusively employed as a trolling technique to start a whirlwind of drama, and occasionally as an excuse to scream at people to either stop mentioning privilege ever again, or to scream at them for having privilege. And/or as a joke about social justice tumblrs. Of these reasons, only the last is tolerable.
why was what bt was doing calling one wrong?
If I understand this correctly: I'm taking Drewbear at his word that this phrase was used totally out of any discernible context. If so, I would be extremely surprised if this wasn't an attempt to start drama. At best it's cluelessness - whether a genuinely meant clueless question, or an attempt at genuine humor - but in context of previous annoying shit this user pulled, I'm not willing to give them the benefit of the doubt.