You might get an error that won’t allow you to use YouTube, saying “Get Google Play Services”.
The easiest thing to do in order to get rid of the error is to power off your smartphone/tablet and start it back.
From what I’ve noticed, the error is related to not being able to sign-in into your Google account, which is odd since an Android user should be always logged into a Google account if he is using YouTube, Gmail or other services.
Anyway, if you just restart your device, you should not encounter this issue anytime soon.