He fails to understand not only the simplest sarcastic jokes, but also regards Penny's sadness over her break up with blatant confusion. That isn't to say Sheldon doesn't have a conscience; he's simply more likely to do what's scientifically ethical rather than morally and socially ethical (break into Penny's home to organize her things).
Sheldon is very obsessive compulsive and as a result has a schedule he must stick to (such as going to the comic book store on certain days, taking a certain path to work, eating specific food items on specific days, or knocking on the door a certain number of times while repeating the person's name he is seeking with a particular frequency).
No one else can touch his food, or it is thrown out. He refuses to sit anywhere other than his designated spot on the couch; other than for the optimal characteristics of the cushion and location he spouts off, this is part of his refusal to accept change, just like with the extra dumpling he couldn't reconcile. If Sheldon is complicit in a lie, he must exhaust all of his efforts to make it believable.
Sheldon has a system of strikes he places on someone if something is done by this person that violates his rules. He rambles on about his imaginative ideas and theories, but does not listen to his friend concerning his research. Sheldon cannot drive an automobile, and needs Leonard to take him places; he feels someone of his intellect doesn't need to learn how to drive. He has childish qualities that extend beyond even his friends' shared interests in comics, science fiction, computer and video games, and toys, as he must get his way (e.g., naming the Caltech Physics Bowl team) and needs his mother to care for him when he is sick.
Among the guys, he shows the least interest in women. As a corollary, it is apparent that he believes everyone else to be intellectually inferior to him, including fellow physicists and even Isaac Newton.