Elon Musk randomly tweets "Ethereum", which was quickly followed by a "jk" tweet reply. Vitalik Buterin responded to the original "Ethereum" tweet by asking Elon to attend Devcon in October. Elon replies "Stop giving away free ETH! 🤣🤣", alluding to Vitalik's twitter username that was put in place when free crypto giveaway impersonation scam bots were popular on Twitter.
More interestingly, Elon asks Vitalik what should be built on Ethereum and Vitalik replied with 5 different ideas: https://twitter.com/VitalikButerin/status/1123136930177118209.