I think it has to do with the phallic imagery and the implied violence in the upward motion. If you turn that hand upside-down, it looks like a flaccid penis and testicles, and this is equally offensive in other cultures. Be careful of the hand signals you use in foreign countries. Thumbs-up is the same as the middle finger in some countries.
User Detail :
Name : carlo, Gender : M, Sexual Orientation : Straight, Race : Asian, Religion : Agnostic, Age : 24, City : toronto, State : NA, Country : Canada, Education level : Over 4 Years of College, Social class : Middle class,