It's easy for someone in your home to interrupt your Chromecast stream and play something of their own, but you can always retake control... right? Well, don't count on it. Analyst Dan Petro has built the Rickmote Controller, a proof-of-concept device that hijacks Google's media stick to play everyone's favorite Rick Astley video (and theoretically, any media) on loop. The Raspberry Pi-based box simply floods the Chromecast with WiFi disconnection requests, kicking the adapter into its setup mode; after that, it's easy for the Rickmote to make its own connection and deliver non-stop '80s pop.
You might not see a fix for this behavior any time soon. Part of the Chromecast's appeal is its easy configuration, and altering the disconnection response might create more headaches than it solves. As it stands, you won't have much reason to worry. Even if pranksters build gadgets like the Rickmote, they'd still have to get within range of your Chromecast's WiFi -- if someone tries to rickroll you through your TV, you'll probably catch them in the act.
Raspberry Pi A/B