You can either choose to trust Part 1 or Part 2, I'm just so lazy to summarize it. :/

The people who is reading this, please don't copy 70% of it. I know who you guys are, so you better watch out. >:/

Please be truthful & be creative. Don't just copy copy copy.

Warning: 99% of the following contents may not be 100% true.

Part 1: 

Blood Type A: 
Positive Traits: Conservative, introverted, reserved, patient, punctual and inclined to be perfectionists. 
Worst Traits: Obsessive, stubborn, self conscious and uptight. 
Type A's are said to be considerate of others and loyal to a fault. They can also be secretive and reluctant to share their feelings.

Blood Type B: 
Best Traits: Animal-loving, creative, flexible, individualistic, optimistic and passionate.
Worst Traits: Forgetful, irresponsible and self-centred. 
Apparently, Type B men have a negative reputation in Korea since their often selfish, unreliable and often prone to anger.  Luckily their bad boy image makes them attractive to woman!

Blood Type AB: 
Best Traits: Cool, controlled, empathic, introverted and rational.
Worst Traits: Aloof, critical, indecisive and unforgiving.
Type AB's are said to be rational and good with money. Although inclined to be distant, they prefer harmony and as such, work well with mediators. 

Blood Type O: 
Best Traits: Ambitious, athletic, robust and self-confident. 
Worst Traits: Arrogant, insensitive, ruthless and vain.
They tend to be outgoing, expressive and passionate, but can also be overly competitive.

Part 2:

Type A

"People with blood type A have a deep-rooted strength that helps them stay calm in a crisis when everyone else is panicking. However, they tend to avoid confrontation, and feel very uncomfortable around people. A types are shy and sometimes withdrawn. They seek harmony and are very polite, but all the same feel that they never really fit in with others. A types are very responsible. If there is a job to be done, they prefer to take care of it themselves. These people crave success and are perfectionists. They are also very creative, and the most artistic of all the blood types, most likely because of their sensitivity".

Type B

"People with blood type B are the most practical of the blood groups. They are specialists in what they do. When they start a project, they spend extra time understanding and trying to follow directions than others might. When they are doing something, all of their attention is focused on it. They tend to stick to a goal and follow it through to the end, even if it seems impossible. They tend to be less than cooperative, as they like to follow their own rules and their own ideas. They are individualists. B type people pay attention to their thoughts a little more than their feelings, and therefore can sometimes seem cold and serious".

Type O

"People with blood type O people are outgoing, energetic and social. They are the most flexible of the blood types. They easily start up projects but often have trouble following through because they give up easily. They are flighty and not too dependable. O types always say what's on their mind. They value the opinion of others and like to be the center of attention. Also, people with O blood are extremely self-confident".

Type AB

"People with blood type AB are hard to categorize. They can have characteristics on both ends of the spectrum at the same time. For instance, they are both shy and outgoing. They easily switch from one opposite to another. AB people are trustworthy and responsible, but can't handle it when too much is asked of them. They don't mind doing favors or helping out, as long as its on their own conditions. People with this blood type are interested in art and metaphysics."

A is most compatible with A and AB.

B is most compatible with B and AB.

AB is most compatible with AB, B, A, and O.

O is most compatible with O and AB.