FOB: an acronym for "Fresh off the boat." A noun used prejoratively to refer to Asians who have either recently arrived to the U.S. or have been in the U.S. for a while, but have resisted acculturation. It is also used as an insult to denigrate Asian-Americans who do not fit into a social group, or display behavior similar to a recent immigrant.
I learned the term FOB from an Asian-American classmate in 1992 while I was in the seventh grade at Walter Reed Junior High School in North Hollywood, California. The use of this term seems to be limited to Asian-Americans and Eurasian-Americans about other Asians and Asian-Americans, although it is used publically even when members of other races are present. This term is not limited to any one Asian-American group. The FOB stereotype often consists of wearing clothing different from the norm, a general disregard for appearance, the frequent use of their native language, in addition to either a heavily accented English or the lack of knowledge of English.
The meaning of "Fresh off the boat" may have arisen from the images of immigration popular in American culture. Often on the news, particularly in California, one will see a boatload of Chinese refugees stranded off the coast. Most recently, the movie Lethal Weapon 4 has taken advantage of this motif. Likewise, before planes, the most frequent method of immigration was through seafaring. Thus, a recent immigrant would literally be "fresh off the boat."
I believe the term FOB arises from the Asian-American perception that other Americans lack the ability to tell Asian groups apart, and that FOBs often perpetuate negative stereotypes in other people's eyes. FOB is used as a means to distance oneself, from both the stereotypes and the people, keeping with the separation of Asian and Asian-American social groups that I observed and participated in while in high school. FOB is handled as a serious insult, and is used as a means of social control, especially among American-born Asian-Americans.