DOCTOR [to LANG]: Don’t be smug with me. Now, I’ve already explained my condition. I may be behaving like a manic barometer, but don’t shrug off help when it’s offered. You can’t afford to.
LANG: I thank you for your offer, Doctor, but frankly, I find you unreliable.
DOCTOR: So’s most currency. Doesn’t stop people spending money wisely.
-Doctor Who episode “The Twin Dilemma”