A close second:
lawl who doesn't <3 the janitor? :P
I think the Swiss Army Knife might be the most successful, after many generations of crossbreeding.
You have obviously never come in contact with the Sprife: The Ultimate Eating Utensil.
As long as you don't introduce dangerous cross-breeds...
http://xkcd.com/419/
That was awesome.
A close second:

lawl who doesn't <3 the janitor? :P
I think the Swiss Army Knife might be the most successful, after many generations of crossbreeding.
You have obviously never come in contact with the Sprife: The Ultimate Eating Utensil.
As long as you don't introduce dangerous cross-breeds...
http://xkcd.com/419/
That was awesome.