This happens when you are having sex with a girl doggy style. You take one of your thumbs and rub her butthole until you loosen it up to penetrate her butthole with your thumb. Once you get her butthole looser then you insert your other thumb. So at this time you have both thumbs inserted into her butthole and you pull your thumbs in a east/west direction and stretch her butthole out. Now you have successfully stretched the rubber band.
by Heath "Rubber Band Man" April 09, 2013