Is it me or my self esteem?

My self esteem is increasing bit by bit... But for some reason I'm still not the best at accepting compliments. There was this guy in class who I thought was cute, but not SUPERcute to where I'd date him. He was like, "Hey you're cute." Like whoopy-doo, just outta the blue he approaches me with that line. Then he goes so far as to say, "And I love your smile. Smile again. Please smile again." I mean I don't know if its due to my lack of attraction to him, or what, but i always kinda come off as rude. Its not as to where he saw my full reaction, but yea I don't know. But i do this with lots of guys, even cute ones. I guess I often feel they don't mean it. Then again... Well I don't know. But when he told me to smile, i reacted like this...

Luckily, he didn't see this last part, at least I don't think. I'm not sure why i react so, so... SARCASTICALLY? I'm happy that he even gives me the time of day. Yet my facial expressions often come off as if I don't appreciate it. Maybe i have a biitch-reflex or something. Lol its like guys compliment me and in turn they get this:

Do you think its a result of my somewhat low self esteem or am I just being bitchy? I'd really like some good advice rather than be bashed.
Its you and your attitude.
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Its your low self esteem.
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Is it me or my self esteem?
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