The black man who "sells" Dennis and Dee the AR-15 is the same man they buy "One rock of crack" from in season 2 episode 3 'Dennis and Dee Go On Welfare'
The episode title is an homage to the season 1 episode "Gun Fever" where the gang is split on whether or not to buy a gun for the bar.
Dave Foley, who played a high school principal in an earlier season, returns as a middle school principal