the word to describe when you are not up, but rather, quite down to partake in usually obnoxious shenanigans. Only, said person does not want to merely say "down" but assert their creatively intelligent IQ level by combining the sounds of ACDC and Mariah Carey in one stunningly grotesque way.
Stranger: "Hey man, you wanna throw water balloons over at the dog park?"
Fun Stranger: "I'm downsies."
Fun Stranger: "I'm downsies."