How about...
Shimano Vs Campagnolo - makes the christian crusades look like a schoolgirl pillowfight.
ILTB Vs anyone who subtly hints at there being any class separation between different types of cyclists, especially if it involves lycra!

better get your flameproof suits on for that one!
And what about the VC storm that rages unabated in the P&R forum? just like the 300 year old storm on Jupiter, they just keep going round and round and round the same points with no end in sight yet regardless of the consequences it bears no relevance to the rest of us cycling in the real world.
Backpack Vs panniers - we shove sticks in the spokes of cyclists making the 'wrong' choice!
LBS Vs online
Clipless Vs flats
Lycra Vs cotton
Vintage Vs New
Helmet anyone?.... and what about carring a you-know-what (you'll need a CCW permit)
I love coming to these forums for support from my fellow cyclists, we're such a nurturing community...