My pipe exploded..

[masonjs at nrtco.net]

You didn't by chance turn your kill switch off whole the bike was 
running and moving and then turn it back on.   This was a trick with 
the English bikes we rode in my yoot.
With the kill switch activated and the motor being rotated by inertia 
you could load up both mufflers with a gas/air mixture.  When you 
released the kill switch the hot exhaust gases from the fired 
cylinders would ignite the fuel mixture in the pipes and mufflers 
producing a couple of blasts a little better than  that of a 12 gauge 
shotgun.  There were also a couple of nice 5 - 6 foot flames that shot 
out the back.  This could also be done with a car with a standard 
transmission or an old 2 speed automatic.  I never saw this bother a 
motorcycle exhaust but I saw quite a few cars that lost the exhaust 
system from the muffler back and/or the muffler would be split wide 
open.
Small town Saturday night.

Jim