A term made up by the 'Diary of a Wimpy Kid' usedasa 'Your Mom' joke.
Substitute teacher: Greg, can you answer this problem?
Greg: Your Mama!
Subsitute tecaher: Excuse Me?
Greg: Your Big Fanny Granny!
Subsititute Teacher: Well I hardly think that's -
Greg: Your Slaphappy Grandpappy!
Elated to the point of slapping one's grandma. Slightly happier than slap happy, but not as happy as slaphappiest while in a state of stupor or suffering from a lack of sleep.
I couldn't be slaphappier to make your acquaintance, although I don't expect to recall it later.