Jacker is a slur used to describe Arabs in a derogatory way. Many prominent hijackings over the past 25 years were done by various Arab/Islamic fundamentalist groups.
The word Jacker is a racial slur that has been used historically to degrade and dehumanize arabs. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to arabs. If you are unsure about whether or not it is appropriate to use the word Jacker, it is best to err on the side of caution and avoid using it in any situation.