My biggest bugbear?
Folks who join forums without first reading the rules/ethos of the site, and the general 'tone' of the place, to see if *they* will fit in ok, and then moan afterwards when they don't like the way things are, or discover that the established mindset conflicts with their deeply-ingrained 'belief system'!
There seems to be a gross miscomprehension that it's up to the forum concerned to 'accommodate' them (and their, to put it politely, 'challenging personality quirks'), when the very opposite applies.
It's up to YOU to fit in with whatever forum you join, respect the way things are and get on amicably with those in charge, not IT/THEM to fit in with you!
Marco.