I have always wondered about the origin of blonde jokes. All women I know, despite of their hair color, are pretty smart! So, with a little help from Wikipedia, here it is:

The blonde stereotype, the stereotypical perception of blond-haired women, has two aspects. On one hand, over the history, blonde hair in women has been considered attractive and desirable. On the other hand, a blonde woman is often perceived as making little use of intelligence, as a “woman who relied on her looks rather than on intelligence.”

It can be used as a popular culture derogatory stereotype to use hair colour as an indication of intelligence. This stereotype is utilized in blonde jokes.

Blonde hair is also a physical trait often associated with “bimbos,” attractive women perceived as unintelligent or uneducated.

Background
At the same time, people tend to presume that blondes are less serious-minded and less intelligent than brunettes, as reflected in “blonde jokes.” The roots of this notion may be traced to Europe, with the “dumb blonde” in question being a French courtesan named Rosalie Duthe, satirised in a 1775 play Les curiosites de la Foire for her habit of pausing a long time before speaking, appearing not only stupid but literally dumb (in the sense of mute).

The notion of “dumb blonde” has been a topic of academic research reported in scholarly articles and university symposia, which tend to confirm that many people hold to the perception that light-haired women are less intelligent than women with dark hair.

Dumb Blonde
The dumb blonde stereotype (and the associated cognitive bias) may have some negative consequences and it can also damage a blonde person’s career prospects.

Support
Gentlemen Prefer Blondes (a comic novel, a Broadway musical, and two films) explores the appeal of blonde women. The film starred Marilyn Monroe as the blonde and Jane Russell as her wise brunette friend. The Encyclopedia of Hair describes Monroe’s role as that of “a fragile woman who relied on her looks rather than on intelligence—what some people refer to as ‘dumb blond’.” At the same time, in the film she demonstrates a certain amount of wit regarding her life position expressed in her hit “Diamonds are a girl’s best friend”. And when her fiancé’s father (who initially disliked her but eventually was won over) asked her why she pretends to be dumb, she answers that men prefer this way.

Many blond actresses have played stereotypical “dumb blondes”, including Judy Holliday, Jayne Mansfield and Goldie Hawn, best known as the giggling “dumb blonde”, stumbling over her lines, especially when she introduced Rowan & Martin’s Laugh-In “News of the Future”.

In the American sitcom Three’s Company the blond girl (originally Chrissy played by Suzanne Somers, and later Cindy and Terri) is sweet and naïve, while the brunette (Janet played by Joyce DeWitt) is smart.

In the TV Series Glee, actress Heather Morris plays Brittany Pierce, a cheerleader who is also a member of the glee club New Directions. Brittany is a stereotypical dumb blonde; sexy and beautiful, but with less intelligence.

Blonde Jokes
There is a category of jokes called “blonde jokes” that employs the dumb blonde stereotype. It overlaps at times with the “sorority girl” series of jokes and the “Jewish American Princess” series of jokes that generally portray the subject of the joke as promiscuous and/or stupid.

Blonde jokes have been criticized as sexist by several authors, as most blondes in these jokes are female, although male variations also exist. Research indicates that because of this, men find blonde jokes significantly more amusing than women say they do

Many blonde jokes are variations on other stereotypical jokes. Blonde jokes nearly always take the format of the blond(e) placing himself or herself in an unusual situation, performing a silly act because he or she misconstrued the meaning of how an activity is supposed to play out, or making a comment that serves to highlight his or her supposed lack of intelligence, lack of common sense, or cluelessness, or promiscuity.

10. Question: If a blonde and a brunette fell off a building, who would hit the ground first?
Answer: The brunette – the blonde would have to stop for directions!

9. The assistant asked the blonde if she would like her pizza cut into six pieces or twelve.
“Six please” she said, “I could never eat twelve!”

8. A blonde was walking down the road with a healthy looking pig under her arm. As she passed the bus stop, someone asked,
“Where did you get that?”
The pig replied, “I won her in a raffle!”

7. A person went into the office kitchen one morning and found a new blonde girl painting the walls. She was wearing a new fur coat and a nice denim jacket. Thinking this was a little strange, he asked her why she was wearing them rather than old clothes or an overall. She showed him the instructions on the tin, “For best results, put on two coats”.

6. Two blondes were in a parking lot trying to unlock the door of their car with a coat hanger.
First Blonde: “I can’t seem to get this door unlocked!
Second Blonde: Well you better hurry up. It’s starting to rain and the top is down!

5. Three blondes were walking through a field when they came across a set of tracks. The first blonde looked down at the tracks and said,
“I think they could be bird tracks.”
The second blonde went to look and said,
“No, I think these are deer tracks.”
They stepped aside and the third blonde went over to the tracks. She looked down, then got run over by the train!

4. A blonde asked someone what time it was, and they told her it was 4:45. The blonde, with a puzzled look on her face replied, “You know, it’s the weirdest thing, I have been asking that question all day, and each time I get a different answer.”

3. A blonde was driving down the road listening to the radio and was quite upset when she heard blonde joke after blonde joke. A little way down the road, she saw another blonde out in a field rowing a boat. The blonde stopped her car and angrily jumped out yelling, “You dumb blonde bimbo! It’s blondes like you that give the rest of us a bad name! If I could swim I’d come out there and give you what’s coming to you!”

2. A blonde and a redhead went to the bar after work for a drink, and sat on stools watching the 6 O’clock news. A man was shown threatening to jump from the Brooklyn Bridge, and the blonde bet the redhead $50 that he wouldn’t jump. Sure enough, he jumped, so the blonde gave the redhead $50. The redhead said, “I can’t take this, you’re my friend.”

But the blonde insisted saying, “No. A bet’s a bet.”

Then the redhead said “Listen, I have to tell you that I saw this on the 5 O’clock news, so I can’t take your money.”

The blonde replied “Well, so did I, but I didn’t think he would jump again!”

1. A dumb blonde was really tired of being made fun of, so she decided to have her hair she would look like a brunette. When she had brown hair, she decided to take a drive in the country. After she had been driving for a while, she saw a farmer and a flock of sheep and thought, “Oh! Those sheep are so adorable!”

She got out and walked over to the farmer and said, “If I can guess how many sheep you have, can I take one home?”

The farmer, being a bit of a gambler himself, said she could have a try.

The blonde looked at the flock and guessed, “157.”

The farmer was amazed – she was right! So the blonde, (who looked like a brunette), picked one out and got back into her car.

Before she left, farmer walked up to her and said.

“If I can guess the real color of your hair, can I have my dog back?