1. To take a perfectly good idea or plan and ruin it.
2. To take anything awesome and turn it to poo.
3. Stealing someone's idea and claiming it as your own, but doing so in such a manner that the initial idea is turned into something so dumb that one could only think that a mentally handicapped preschooler came up with the idea.
Person 2: "Yeah, you always have such great ideas. I aspire to be you. They are both going to be so much fun."
Person 3: "Wait, whatever you do, don't let that guy (person 4) hear, he will joshify your ideas for sure!"
Person 1: "Thanks, man! I completely forgot how much I hate that kid. He always steals people's ideas and ruins them."