Imagine the Jays changed their names to the Muricans and had a jersey with a caricature of an overweight,  Southerner with a monster truck wearing a ball cap and all the players were mandated to use Lynyrd Skynyrd for their walk up music.  

Urban dictionary:
."It is generally seen as a derogatory yet humorous way to describe most Americans: fat, lazy, gunwielding, war loving, horse riding, saloon fighting, beer drinking, sex wanting or etc."

Get it now?  You wouldn't call a Chinese person a name that rhymes with "rink" or a spaced out driver, math whiz, eat anything, table tennis expert would you?