I've been very lucky in my life to get to shoot some very fun guns. As was mentioned above, when in the Army I got to shoot a Tommy gun on full auto. That was hoot, and then there was the M3 "Grease Gun" and the 9mm Swedish "K" that was fun too!
Probably the most fun though were the guns in the Cobra's flexible nose turret. The "7.62 NATO minigun" at 4,000 rounds per minute and the 40mm grenade launcher at 450 rounds per minute were a total blast (literally) to shoot.
These days, I get my kicks with my Mini-14.
Fear is a reaction..............Courage is a decision