There is a certain type of woman that can go into an established close-knit group of men, insert her sexuality within, and destabilize everything. In this episode of The Big Bang Theory, that woman is Dr. Elizabeth Plimpton. Unfamiliar with the opposite sex, Sheldon used his limited knowledge to prepare for her arrival and stay at his and Leonard's apartment. Both Sheldon and Leonard come off as awkward with Elizabeth, but were not met with any expected negative consequences, despite their blatant lack of social grace.
Unexpectedly, Elizabeth was receptive towards all the men. In fact, too receptive. Sheldon decided that amongst his many ways of being a good host, one such approach would be for him to spend the night on the couch, so that Elizabeth could sleep in his room. Unbeknownst to him, he did not actually have to make this sacrifice, as Elizabeth and Leonard did not need him to give up his room. She did not just stop there. Her dialogue at the cafeteria lunch table led to Halo night needing to be canceled, as Raj decided that he needed to lock the door on his friends.