Stolen from another site:

The Mistress

Herbie and his wife were having dinner at a very fine restaurant when this absolutely stunning young woman comes over to their table, gives the husband a big open mouthed kiss, then says she'll see him later and walks away.

Herbie's wife glares at her husband and says, "Who was that?"

"Oh," replies the husband, "She's my mistress."

"Well, that's the last straw," says the wife angrily, "I've had enough. I want a divorce!"

"I can understand that," replies her husband, "but remember, all our perks come from my job. If we get a divorce, it will mean no more shopping trips to Paris , no more wintering in Barbados , no more summers in Tuscany, no more Jaguar and Merc in the garage and no more yacht club. But the decision is yours."

Just then, Herbie's best friend enters the restaurant with a gorgeous babe on his arm.

"Who's that woman with Mike?" asks the wife.

"That's his mistress," says her husband.

The wife pauses for a moment, looked up an says, "Ours is prettier,".