In the following Washington Post's article (Feb. 13) reporting the outcome of CPAC 2011, I found the phrase if you must know.
I think this phrase means though it may not be essential knowledge that you are supposed to have, or just for your reference. What is the difference of nuance among if you must know, you may know, and you might know, which is difficult for non-native English learner to discern?
The three-day Conservative Political Action Conference ended Saturday afternoon with a meaningless presidential straw poll (if you must know, libertarian gadfly Ron Paul won for the second year in a row).
Best Answer
"If you must know..." typically introduces a fact that the speaker is reluctant to reveal. It's a little rude, as it implies that the listener is being nosy (intrusive). E.g., "Why weren't you at work yesterday?" -- "If you must know, I was visiting a family member in the hospital."
"You may/might know" introduces a fact somewhat apologetically. My understanding of it is that it's apologizing for wasting the time of the listener if they already know the fact. I think it also implies that the speaker isn't presuming that the listener is ignorant of the fact (to prevent insulting the listener's intelligence).