Four Footer is a slur used to describe Mexicans in a derogatory way. Ususally used when referring to illegal immigrant workers. "I'm gonna go down to 7-11 tomorrow morning, to pick up a four-footer." Because mexicans are short.
The word Four Footer is a racial slur that has been used historically to degrade and dehumanize mexicans. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to mexicans. If you are unsure about whether or not it is appropriate to use the word Four Footer, it is best to err on the side of caution and avoid using it in any situation.