Director: Terry Jones
IMDB: http://www.imdb.com/title/tt1727770/
Wiki:

Synopsis:
a group of aliens who endow an earthling with the power to do 'absolutely anything' to see what a mess he'll make of things -- which is precisely what happens. There's also a talking dog named Dennis who seems to understand more about the mayhem that ensues than anyone else does.
Cast:

Robin Williams - Dennis
John Cleese
Michael Palin