You assume people (most people anyway) would have some level common sense, but every now and then you meet someone with such a lack of that it simply renders you speechless. There is nothing to say except to do a facepalm as they stare at you wondering what's the problem.
I'll forgive the occasional absentmindedness. However, when it happens so
often to the point that I can't help but say "really?", that's where
I draw the line.
You think you know someone, but then they throw something out of the left field
and prove once again that you should never make assumptions.