It happens, it's not the worst I've seen, but it is, as you say, very impolite. That's his problem not yours... do not accept his burden!
p.s. you may wish to alter your privacy settings. 
Unprovoked attack
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Below is an unprovoked attack made by a chess.com user on the "daily puzzle" thread. I like to belive that there is a level of polite sociablity around this site and admire the way most people interact with each other. I just can't wrap my head around this example of poor sociabiliy that was unprovoked and just short of vindictive. Why would this man try to belittle a stranger who just overlooked something very small?
http://i240.photobucket.com/albums/ff209/TehPantz/Badattitude.jpg