I think that silly kids' jokes can sometimes tickle better than sophisticated grown-up ones (though I love those too). Groan at will:

Why did the old man fall in a well?
Because he couldn’t see that well!

Why did the actor fall through the floorboards?
He was going through a stage...

Why did the scarecrow win a Nobel prize?
He was outstanding in his field!

What did the three-legged dog say when he walked into a saloon?
“I’m looking for the man who shot my paw!”

(Sorry, I have no more coats...)