While this video is somewhat long (over 4 minutes), it is beautiful. 
I've snorkeled many a reef, though I can't quite get the nerve to
SCUBA.  And if I saw something like this... well, my wet-suit would be
wet due to a bodily function that it wasn't designed for.  The incident occurs at the 3:30 mark...

While I know that humpback whales don't eat people (at least on purpose), something the size of a small train plowing passed me when diving would freak me out.

Video posted by westh2o on October 24, 2011.

Click here for more cool animal videos!