The truly ultimate responce to any kind of stupid or annoying "why" question, or simply to a question you cannot answer.
That answer will totally piss off annoying kids who ask too many questions.
See also: because you're gay.
Kid: Why did the dinosaurs die out?
Tour guide: Because you touch yourself at night.
Son: Why do you drink so much, dad?
Dad: Because you touch yourself at night!
Little brother: Why don't you ever let me into your room?
Big brother: Because you touch yourself at night, you little brat!
Someone who jumps from one relationship immediately into another one.
Serial monogamists can not stand to be alone and often suffer from vast commitment and insecurity issues.
Because they jump into relationships immediately after the previous one has ended, serial monogamists typically don't take the time to reflect on their behavior or why their previous relationships failed; thus, they end up making the same relationship mistakes over and over again.
Person 1: Damn, Dustin already has a new girlfriend?! It's only been two weeks since he broke up with his fiance! I think he's a sociopath.