The Big Bang Theory Season 2 Episode 6
The Cooper-Nowitzki Theorem
After an open house night at the University with grad students, an obsessive student Ramona Nowitzki (Riki Lindhome) likes Sheldon and makes her way into becoming his girlfriend / assistant. Although Romana starts off being a good influence in high life, she soon begins to cut into his social life (nomore Halo, paintball, comic books, etc). Ramona even soon gets jealous of Penny.
When Sheldon realizes he's dating Romana, he tries to get Leonard to help him get rid of her. The final straw comes when after Sheldon solves his scientific problem, she wants credit for helping him work on it by calling it the "Cooper-Nowitzki Theorem." He immediately kicks her out and tell her to "get out!"
The episode ends with another young woman that approached Sheldon in the same way Romana did and the cycle begins again.