Seems to me that the tire was installed incorrectly at the LBS. Easy to do if your in a hurry as most LBS are. To have a side wall blow out where the tire comes off the bead and the tube then comes out and goes bang means the tire was either the wrong rim size or installed wrong. There is a line (witness mark) on the sidewall that goes all the way around the tire and should be seen just above the rim, as well as evenly spaced above the rim. If its not that means some part of the tire is not seated properly on the inner rim edge.
The following is from Sheldon Brown:
Blowouts are sudden losses of air, usually accompanied by a loud BANG! Since the inner tube is just a rubber balloon, if you pump it up outside of a tire, it will stretch bigger and bigger the more air you put into it, until it pops. The inner tube will not take much pressure by itself, it needs to be held inside of a tire to get up to full pressure. If the tire doesn't hold the tube in all around, the tube will pop.
Last edited by Hairy Hands; 06-23-12 at 10:02 AM.