T. Leuthard has a list of excuses if you're challenged while photographing on the street.
"I'm a photo student and our teacher wants us to shoot people. He is very tough…"
"I work on the 100 Strangers project (www.100strangers.com)…"
"I love your beautiful eyes…"
"You have an interesting face…"
"I love your style…"
"You are hot. Can I have your phone number…?"
Here's my first one:
"I am an undercover policeman. We suspect a nest of terrorists in this area, and one way of finding suspects is to see who will protest when we take their picture."