Good question... and no it isn't bad not to know.

Basically it derives from the tin foil hat wearers who see a conspiracy in everything. Applied to fandom it is a term for people who think only their version of a situation is true and everybody else is wrong.
So, sayinf J2 is a fact and everyone who says different is a hater would be a sign for a tin hat.. *g*
Of course there is a lot of mockery.

Here is a little explanation fandomwank wiki