The YouTube tags your trying to use don't appear to be installed on this particular forum. ScubaBoard is using vBulletin ... This looks like PhPBB if I'm not mistaken.
I looked through the FAQ and there was no mention of embedding media files other than images hosted remotely.
Still, it's no big deal just to put a direct link in place.
I did a quick search on YouTube for the keyword "gun" and found this video:
http://youtube.com/watch?v=ZXkrS48FFYU
Now, no flames please, I'm not trying to send any political messages here, I just figured it was a parody of Home Shopping Network or QVC until the political stuff came up at the end.
Interesting comments appear below it!
Anyway, it's the easiest method to link to a video without having HTML or BBCode to access such media.
... adding to ...
I also looked into the possibility of using HTML to embed a shockwave object, which might work, but HTML is turned OFF by the Administrator, which is a general safety factor.
Still, I did have to share one more YouTube video I saw that really cracked me up, it's called Gun Fight:
http://www.youtube.com/watch?v=Iazttg8_E9g
Enjoy!