Personality is important. You could also think about something that might simply suit the content you are doing or something in your life or perhaps both! Personally I've gone through some really hard times lately and ended up having to move a a couple states away to try to get things together. I also started making YouTube videos as an outlet, something I had control over and a way to take control of my life if you will. Because of this my outtro is "Play games, and take control." It's a play on words, since you "control" games. But it's also got the idea behind it that you can't let life control you, you need to control it.
As you can see, I took theme of my channel and combined it with my reason for making the channel in order to come up with an outtro.