Another for the list...completely inconsistent scales at airports.
At JFK I check in one piece of luggage and it registers at 49lbs. This piece of luggage is completely untouched (other than me lifting it by the handle

) when I check it in at ORD a couple of days later and it now weighs just over 51lbs. Agents says it is overweight and I must repack my bags or pay $50

You end up with one of those 'oh yeah, sure it was fine at JFK' type agents.