These "counter-rage" incidents need to be put into perspective with the whole story being told, people dont just walk up to the counter and start throwing staplers.
HOWEVER ... people DO just walk up to the counter, blithely unaware that they are late/stupid/smelly/intoxicated etc. and when they get told of this fact, THAT is when they get upset.
Agreed, people don't just walk up to the counter and start throwing staplers ... and check in staff don't just deny boarding for the hell of it!