Mathematics

I like the last one best!

ROMANCE MATHEMATICS
Smart man + smart woman = romance
Smart man + dumb woman = affair
Dumb man + smart woman = marriage
Dumb man + dumb woman = pregnancy

OFFICE ARITHMETIC
Smart boss + smart employee = profit
Smart boss + dumb employee = production
Dumb boss + smart employee = promotion
Dumb boss + dumb employee = overtime

SHOPPING MATH
A man will pay £2 for a £1 item he needs.
A woman will pay £1 for a £2 item that she doesn't need.

GENERAL EQUATIONS & STATISTICS
A woman worries about the future until she gets a husband.
A man never worries about the future until he gets a wife.
A successful man is one who makes more money than his wife can spend.
A successful woman is one who can find such a man.

HAPPINESS
To be happy with a man, you must understand him a lot and love him a little.
To be happy with a woman, you must love her a lot and not try to understand her at all.

LONGEVITY
Married men live longer than single men do, but married men are a lot more willing to die.

PROPENSITY TO CHANGE
A woman marries a man expecting he will change, but he doesn't.
A man marries a woman expecting that she won't change, and she does.

DISCUSSION TECHNIQUE
A woman has the last word in any argument.
Anything a man says after that is the beginning of a new argument.

HOW TO STOP PEOPLE FROM BUGGING YOU ABOUT GETTING MARRIED
Old aunts used to come up to me at weddings, poking me in the ribs and cackling, telling me, "You're next." They stopped after I started doing the same thing to them at funerals.