In fairness, I've only been working on bicycles for about three or four months (although I can build a motorcycle from its componant parts) and I'd say I now know more about them than a good 50-60% of the people working behind the counter in my local bike shops. I freely admit I know very little but actually finding out about something before opening ones mouth and spouting off about it seems to be a rarity in this particular field.

The best one to-date was two guys in the same bike shop insisting point blank that 700C tyres fit on 27" wheels. Even when I pointed out there is an 8mm difference in rim sizes between the two wheels.