Only one, but it sure takes a shitload of light bulbs!
or
Half a worm.
or
It's someone who knows how to play the bagpipes, but doesn't.
or
Because E.T. eventually went home!
or
The Flea Stooges!
or
Drinking, bathing, washing, swimming, etc.
or
Fryday
or
Bozo The Clown has real hair on his head.
or
A hoarse fly!
or
Never lick the spoon!
or