It's been over 8 years and both capturing game footage and Youtube have come along way.
Click here for a vastly improved, 2015 version of this video!    • Mario Power Tennis Bloopers (Full Ree...  

Original Description
There didn't actually seem to be a good quality rendition of this up on YouTube so, as Mario would say: Here we go
This is Blooper Reels 1 and 2 from the credits of the game, given a rough edit together and cutting out the actual credits.
Just the outtakes