Yeah, I think for the true believers, FMF's first post really captures a lot of what makes them declare every convention (and, indeed, every meeting) the "best ever." Then there's the fence-sitters and those that don't really 'feel it' like everyone else (I was always in this group, personally) who just agree and nod along or say it with some sarcasm just because it's the only thing that's socially acceptable to do. Who wants to have an argument over whether or not it actually was the best convention ever? I certainly never did. You'll only lose when everyone starts in on the attack and end up getting lectured and scolded and left receiving suspicious looks for a while.
Sometimes it can be difficult to tell the true believers and the semi-doubters apart, just because any appearance other than being a true believer results in punishment in some form or another. This just leaves anyone who doesn't really "feel it" feeling as if they're completely alone with no choice but to just go along.