What a dumb question...I mean, all of these guys in the NBA worked their freaking asses off to get here, and did nothing other than play basketball every day. I don't expect anyone to be some bright valedictorian. Klay's personality is what it is, he seems like a nice guy to me, I guarantee that you're making the assumption that he's a sour puss based on his appearance/body language during games. Truth is, none of us here are in the locker room/gym with Klay and we can't make claims on what his personality is or isn't based on the way he carries himself in games. But it doesn't even matter anyways. I like watching good basketball, regardless of who the players are.
All I have to say is...if you hate Klay's personality, you must have HATED the We Believe team with guys like Stephen Jackson, Al Harrington, Monta Ellis, and so on, haha.