United Airlines staffer pretends bag is too big for carry on

A passenger's bag slides into a United Airlines test compartment with ease, but the employee pulls it out, then sets it down on the test compartment at an angle to prevent it from going in. He shrugs and says "Rules are rules." Why is this staffer purposely stressing out a passenger? Years ago United staff had a reputation for treating their customers with snide contempt. In more recent times they seemed to be on a path of rehabilitation, but institutional sociopathy has crept back.