The Skank Reflex Analysis (2011)

Raj finds himself in hot water with Leonard and Howard after supposedly sleeping with Penny and the latter discovering his fantasies about Bernadette (who also became angry at Raj because of his fantasies, and now has to contend with Howard's feeling of distrust of her as a result). Raj and Penny later talk and it turns out they didn't sleep together because Raj ejaculated prematurely when Penny tries to help him put on his "Protection". Nonetheless, Penny feels that this has damaged her relationship with the guys permanently and decides to move back to Nebraska, as she has not had any worthwhile acting jobs since moving to Pasadena. When she comes over to apologize and announce her intention to move, she gets a call from her manager, informing her that she got a part in a hemorrhoids commercial, prompting her to scrap her plans.

Meanwhile, Sheldon has appointed himself the captain of the guys' paintball team. When they are at another of the university's tournaments where they fight against other departments, their team falls apart because of Leonard, Howard and Raj's lack of enthusiasm due to everything that has gone on with Penny. Sheldon, blaming himself, puts down his paintball gun and walks outside, proclaiming that geology isn't a real science. Following that, he is promptly shot several times. Leonard, Howard, and Raj immediately rush out to avenge Sheldon's "sacrifice" and even manage to claim the victory for the physics department.

Recurring character: Christine Baranski as Dr. Beverly Hofstader

Title reference: Amy's term for Penny's promiscuous behaviour that is responsible for releasing dopamine.