Here's how you can force, without jailbreak, iOS not to play YouTube videos using the native iOS application

  In iOS, Apple included a special application that allows iDevice owners to watch videos from the famous video sharing website YouTube. Unfortunately, the application does not have such a great functionality, but those from YouTube had the initiative to launch a web version of their website that works better than the native iOS application and allows us to watch the clips in better quality. However, iOS forces us to watch all videos in the YouTube application, but this restriction can be removed very simply and easily.

  All you have to do is to go in Settings> General> Restrictions and disable YouTube from there, and all the movies found in various applications, or even in Safari, will be opened using the browser of those applications or even Safari. Activating this option will completely hide the YouTube application and to bring it back to Springboard you must reactivate it from the same settings menu.