"yeah right"

when I ask for the number, lots (not necessarily
most, but a good number) of girls initially say
"Oh, my number's disconnected." or "I just moved,
and haven't gotten new phone number installed
yet." However, when I give a cocky response, or
even if i just say "yeah right", they IMMEDIATELY
concede and give me their number... and lo and
behold, it works.