There are so many wonderful examples of these, please share your favourites. Bonus points for links.
I remember one when OP was annoyed if the cost of children's birthday gifts weren't higher than the cost of hosting the party per child.
And the classic from a few weeks ago when OP thought it was ok to block the shared driveway and thought their neighbour who lived at the end was the unreasonable one.
I bet there are better ones out there though...