A term made up by the 'Diary of a Wimpy Kid' used asa '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!
Word originating from Afrikaans meaning "lazy". Often used to denote persons such as teenagers, a person not pulling his/her weight - a lazy ass (lit.)
That guy is a real slapgat when it comes to completing the paperwork, he never does it on time.