Spitting is the act of forcibly ejecting saliva or other substances from the mouth. In Europe and North America, it is normally considered rude, and a social taboo. It is sometimes considered a competitive and fun activity amongst youths.
Spitting upon another person, especially onto their face, is a universal sign of anger, hatred or contempt. It is possible to transmit infectious diseases in this way.
In London, transport workers who deal with the public have recently been given equipment to collect saliva when they are spat upon by irate passengers. The police can then analyse the DNA of the offender.