First used on the tv show Archer, stir friday is when a couple plans a friday to make stirfry together. These strange events dont make much sense to normal, actually fun people, but if you were to ask the couple why they do this they would most likely reply "Because we like to have fun together and try new things." The real reason these events exist is to make boring people feel like they have accomplished something exciting and to distract from how truly gay they are.
A: "Is Chuck coming to the bachelor party?"
B: "No, he said he can't miss stir-friday again, its his turn to cook"
A: "Wow, thats weak... he was so fun before he met Judy"