I agree completely with Ramesh that “check your privilege” is leftist for “shut up.” I’d also note that the words “check your privilege” are almost always uttered by some of the most privileged people on earth — Ivy League academics (and students), upper-class urban liberals, and members of the liberal creative class. This is not a cry from the oppressed but instead a demand from the culturally, politically, and economically powerful.
Demanding that a white Princeton student be deferential to his liberal betters does exactly nothing to improve the lives of the poor or to change history or to even change the already-radical institution he attends. Instead, it’s a method of petty power politics, where a certain segment of the liberal elite teaches itself to win arguments through shame and censorship rather than through reason and logic.
“Check your privilege” is a statement with only as much power as you give it. Give it none — not even the power to make you laugh.