When you are watching a video on YouTube, click “Share” and to the right of the embed information is a link to launch a Google Hangout. Select that link, launch a hangout and wait for your friends to join.
Google+ already lets you watch a YouTube video with friends in a hangout, but the process is cumbersome. You have to start a hangout, invite some friends and make them wait while you look for your YouTube video. This new YouTube-based method is much more elegant. [Google+ via The Next Web]