Really, FJ?
The character doesn't understand sarcasm, yet tries to understand sarcasm in multiple story lines, going so far as to ask when he did and did not get it right.
There are at least half a dozen episodes whose main plot is about Sheldon actively trying to understand why people are doing something, yet failing in this endeavor.
*snip*
If Sheldon was just a jerk, it wouldn't be funny. Then the show would be about the life and times of a narcissist. While there are moments of that, if Sheldon was completely self absorbed and rude while knowing what he was doing was unacceptable behavior, yet choosing to do it anyway, he would be completely unrelatable. A villain, like the guy with the lisp.
Instead, he as a blundering genius. An absent minded professor, childlike in his misunderstanding of human foibles. He often acts and is treated like a child by the other characters, and is forgiven of his megalomania as one would forgive a child.
We're devolving a bit from thread, but it's still interesting.
Sheldon really doesn't qualify as Autistic. OCD with social issues? Oh absolutely, to the n
th degree (There are two diagnosed OCD cases in my family...and I'm pretty close to the line

)
I did read about Temple Grandin as per your previous comment. Was a very good reference, so thank you for that education. Again, Sheldon doesn't qualify, and there are some big differences:
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Sensory overload. This is a regular indication of autism, requiring almost a shut-down and reboot (blocking ears, dissociation, hug machine etc). Sheldon enjoys Paintball, Halo and other exciting releases which are in direct conflict with autism symptoms.
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Competitiveness. Sheldon has to win, always, and prove he's the best. Austism sufferers do not normally relate to such egotistic influences (and when he realises he can't do something, like drive a car, he rationalises it's because he's
'too evolved'...)
Where there are similarities:
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Sheldon and temple both find socialising 'boring'. However, Sheldon is sometimes fascinated by people's responses. This however, is sociopathy, not autism (especially when he deliberately provokes emotional responses to see what would happen)
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Sheldon and Temple both enjoy science fiction (however Sheldon then emulates and roleplays such diversions, like his Flash costumes and antics). An autism sufferer would be incredibly unlikely to be so shameless and extroverted.
Sheldon is likely an Obsessive Compulsive Ego-Maniac with sociopathic tendencies. Some symptoms of these issues align with those of Autism, however Sheldon just isn't suffering from that condition.