You might have noticed that sometimes when you shoot someone, they're wearing a mask. For most people it used to be a tight smile (sometimes accompanied by narrowed eyes: you can tell if they're not smiling with their eyes if you cover their mouths and they look angry). Lately, in keeping with the rise in street style blogs, people immediately strike a pose and deliberately DON't smile and hope they look like a model.
The Sartorialist has developed his own mask - head turned 3/4 in the same direction, face pleasant but not smiling - and I got him to drop his mask in September ('I shot the Sartorialist') by saying something amusing. That's a tip that works with children but sometimes grown-ups, too: make them laugh. Charm your subjects.
However, with these two, it didn't work. I ran up to them, gave my card & asked if I could shoot them (note card in hand) & they let me, but at the moment I pressed the shutter, I asked in a friendly tone what it was for.
'We can't tell you that,' they said, and ran off. Uh, okay, never mind then. Have a nice day.