Totoro

I recall reading an incident about carry-on size restrictions from the pre-9/11 era. As part of CO's official policy, if a passenger could bring it on the aircraft, it could count as a carry-on (I am not commenting on pros and cons of the policy). Because CO started installing extended overhead bins earlier than other airlines, they used this flexibility as an enticement for passengers.

At IAD, UA installed baggage-sizing equipment at the shared security check-points that restricted the size of CO passenger carry-on baggage. CO sued because the equipment prevented them from competing by offering less stringent carry-on regulations. IIRC, CO prevailed! ^