You are using a implicit intent, which can match more than one receiver, thus the chooser. You could try switch to an explicit intent model, if you can figure out how to target the youtube activity directly. See developer documentation on explicit vs. implicit intents.
However, it seems the reason for the intent chooser is to let each user decide for themselves which player to use. Is there a good reason you want to bypass this? What if someone has installed a different video player that they prefer?
Edit: To call an explicit intent, you need to know the name of the activity you are trying to start, and you pass additional details as extras i.e.:
Intent intent = new Intent(this, YouTubeViewerActivity.class);
intent.addExtra("URI", Uri.parse("http://www.youtube.com/watch?v=cxLG2wtE7TM"));
startActivity(intent);
However, I totally made up the fact that there is a YouTubeViewerActivity class. As I said, typically if you are asking some outside service, like the YouTube app, to perform an action you use the implicit intent model like you have, so the user has control over what application is used.