To watch videos, I use Mplayer, which works great. But Ubuntu insists on playing every video file it encounters with "Totem", which I guess is a video player.

I use linux primarily on my laptop, and often on travels, where I have no internet access. All Totem does is launch, and say "should I look for a codec ?", and I have to click no before I can close it.
I know that I can choose "Open with mplayer" for various video formats, but every so often I'll have a file with a different extension, and there comes totem.
I do not seem to be able to remove it from my system, which really infuriates me. I left Windows to avoid programs that you cannot remove. :(
EDIT: If I can't remove it, I'd be happy with a solution to make all video files play with mplayer. I don't want to configure "play with mplayer" for every single file extension there is.