I usually go in with the mega cheese like: "Do you know how much a polar bear weighs? Neither do I, but it broke the ice!" This is a fool proof line, cos if they're giving me bad vibes after the question. I'd say "Probably same as you, ya fat £$%$£!" Shameless
"Hey, do you have the time?" Play it off from there. To girls I see often on the bus or subway..."Hey, I see you almost everyday. How come we never talk?" First one works out often. Second one works out ocassionally. ;]