I am surprised to see that Cooper's most famous one-liner is not included above:

I went to see the Doctor, right, and I said to him "Doctor! It hurts when I do this!" (lifts arm).
And he said "Well, don't do that, then".

Short but sweet. Unlike Tommy Cooper, who was 6'4" and looked like an ex-boxer (he was, in fact, an ex-boxer - well, for that portion of his life after he stopped being a boxer that is. Before then he was a pre-boxer and a boxer respectively), although apparently, as a person, he was as affable as he appeared on stage. He was born in 1922 and died, on stage, in 1984.

His comedy was all about delivery. The material was groansome, but the delivery was all. To achieve the full effect of the above line:

1. Prepare a simple-looking magic trick.
2. Grin sheepishly at the audience, as if you are having difficulty.
3. Have difficulty.
4. Break off. Wander around the stage. Blat out a few one-liners at breakneck speed, look sheepish.
5. Go 'hurhur!'.

And repeat.