Beat the heat and come off the streets for an evening of unscripted, off-the-cuff, on-the-fly mayhem with Baltimore’s death-defying, side-splitting, adjective-compounding comedy squad. The Baltimore Improv Group performs tonight with special guest District of Columbia Unscripted Players (yes, that’s “DCUP” to you), who present “Big Ditties,” an improvised musical-comedy attack on the latest Hollywood blockbusters.