1. A term of endearment, often expressed by members of mop-top haired boy bands, but rarely publicly. Often said moments before orgasm.
2. From that Beatles record
example 1): (1st person says): Dude, we get to go to Florida. (2nd person says): KOO KOO KA CHOO!!
example 2): (1st person says): Hey, can you get me the pen? (2nd person says): Koo koo ka choo.