Underwear Karate
This is when you are either feeling tired, are stoned, or are just feeling like doing "karate". This is a very broad term that can be used for anything ranging from a kid who thinks they are doing karate well saying a bunch of "hi-ya" this and "hi-ya" that until they eventually hurt somebody and their parent tells them to stop, to a professional karate master just feeling like doing karate in the hallway on their way to get coffee.
I saw my brother doing underwear karate in his room through a crack in his door.