Leonard: You know what, I'm so tired I can't even think straight. I'm going home. Will one of you guys give this nutbag a ride back later?
Sheldon: You can't go home. You have to take me to the dentist at four o'clock.
Leonard: Oh, can't you take the bus to the dentist?
Sheldon: Of course I can. It's coming back under the residual effects of the anesthesia, that's the problem. Two years ago after a deep gum cleaning, I thought I got on a bus but somehow wound up on a booze cruise to Mexico.
Raj: They put you under for a cleaning?
Sheldon: Yeah, they have to, I'm a biter.