PROVIDENCE, RI ( Associated Press) — Three days before Elon Musk agreed to buy Twitter, the world’s richest man tweeted a photo of Bill Gates and used a crude word to make fun of his stomach. Playful, aggressive, and often juvenile, Musk’s past tweets show how he’s used social media to blatantly discredit his public image as a ruthless billionaire. They may also provide clues as to how Musk will rule the platform he hopes to own. “Look at the feed: It’s everywhere. It’s uncertain. Sometimes it’s just too extreme,” said Jennifer Grigiel, a Syracuse University professor who studies social...