One night a week or month when the bars (usually in college towns) charge a cover and then let patrons drink all the cheap beer they can. You have to get there early to get a pitcher or you're out of luck, they go fast.
"Hey are you going to Dill tonight?"
"Nah, I'm kinda broke, I'm headin to the Madhatter for penny pitchers
"Hey, I heard you coming in at 5am through the window, did you puke in the microwave...!?"
"Ohh maybe...I dunno..I went to penny pitchers