"What's this!?" demands the grandfather.

"It's a condom" replies the grandson sheepishly.

"What do you use it for?" asks Gramps.

The guy is surprised that his grandpa really doesn't know what a condom is, and replies "I use it to keep my cigarettes dry when I smoke in the rain"

To his surprise his grandpa says "That's a great idea," and goes off to the drug store.

He asks the pharmacist for a condom.

"What size would you like" asks the pharmacist.

"Oh, big enough to fit a camel"