Lying

Sheldon is extremely uncomfortable with lying. He doesn't understand the cultural need for creative lying, such as when Leonard tells Penny they're busy Friday night and can't come to see her perform in a workshop production of the musical "Rent". When Leonard explains that telling the truth would have hurt Penny's feelings, Sheldon is baffled and wonders how that's relevant.

Sheldon has attempted to create his own lie, but completely overdid it to the point where he brought in actors, created fictional Facebook pages, and so on (0110).

Penny confided in Sheldon that she had lied to Leonard on their first date about graduating from community college. Sheldon was so disconcerted by having to keep her secret that he temporarily moved out of the apartment. At one point during that ordeal, he told Penny that his inability to keep a secret had cost him a top-security job (0201).

When Leonard asked Sheldon to cover for him when he was going over to Stephanie's apartment, Sheldon could only say to the others in a very stilted voice "Leonard is ... going to the office." His strange demeanor while saying this lie actually roused suspicion, naturally (0208).