A variation on the term "hotbox" meaning to smoke marijuana with friends in a car with all the windows up creating a cloud of smoke in the car.
Hotboxxx however is to perform above stated activity while listening to hip hop legend Freddie Foxxx a.k.a. Bumpy Knuckles
Mickey: Yo fellas let's go hotboxxx my new GTI!
Darryl: Hells yes! I have a duchen to roll and some haze..
Lisa: I got the Freddie Foxxx mixtape ready to go!