A case of Keystone Light beer. 30 cans... Popular at high school and college parties because of the beverage's affordable cost in comparison to other beers. The term "dirty thirty" was coined in reference to the beer's lackluster if not downright "dirty" taste, and quantity of 30 cans of beer in the package. Despite its shortcomings, eager drunkards across the great u.s. of a. are willing keep their costs down on the shillings to shitfaced (s.t.s.) ratio scale so that the former number can be achieved for a lower price.
"Hey Tom's house is open tonight. I'm going to swing by the Shell and pick up a dirty thirty."
"Alright Ladies, this dirty thirty is on the house!"