When I left the office this evening and was waiting by the elevator I was asked, in Mandarin, if I worked for the company whose office I had exited. I responded in the affirmative. Then I was asked if I had a business card. "I'm sorry, I don't have a card," was my response (in Mandarin, using the correct negative for the verb 'to have,' which is different from the negative used for most other verbs).
Bad idea. I should have just shaken my head and pretended not to understand anything. The man started to speak to me in rapid Mandarin, assuming I understood every word he said. When I interrupted to say that I didn't understand he looked crestfallen.