5. Summer Glau
When the guys are on a train to San Francisco in 'The Terminator Decoupling' they notice that star of Terminator: The Sarah Connors Chronicles, Summer Glau, is also on the train. What pursues is the gang (except Sheldon of course) competing over who gets first chance in chatting her up. Raj comes across charming but fails when he realises he is drinking non-alcoholic beer, although that would upset anyone. True to form, Howard creeps her out and ends up with a broken phone when he pushes his luck. Leonard, ever sensible, tries the normal approach with her but sadly just when the train reaches her stop. Glau's cameo is one of the longer ones on the list and it provides us with some great moments. The boys' chat-up techniques are all put under the spotlight to great comic effect, and her reaction to Howard's wildly creepy lines are priceless.