Just walked up, framed them, shot, and moved on. All the exposure settings were in place, so all I had to do was focus and shoot. I was working with a relatively unobtrusive rangefinder, so there wasn't any giant lens pointing at them. I'm hardly an old hand at street photography, but the more I do it, the more I realize that being quick and appearing confident makes a big difference - if you look like you know what you're doing you get away with a lot more than if you try to sneak up slowly.
All that said, there were a fair number of people with cameras wandering about (this was Bryant Park, so more tourist traffic than Washington Square), so I probably had pretty good cover.