Similes compare two things. Because clowns are considered by most to be very funny, the object would also have to be something funny.
Therefore you could say...
A clown is as funny as a medieval joker.
A clown is as funny as a cat barking like a dog.
A clown is as funny as a comedy movie.
Authors pen is the most powerful sword
There were so many amazing plans going through my head for the for the large amounts of money I would soon be making I thought, as I ran as quickly as I could.
