in baseball, "a low batting average," (somewhere around .200) with the suggestion that any player hitting below it ought to feel a bit ashamed, by 1984, said to have been in humorous use in baseball clubhouses c. 1979, from the name of former Pirate, Mariner, and Ranger shortstop Mario Mendoza, who was noted for his defense but whose .215 lifetime batting average routinely left him at the bottom of weekly batting averages. The surname is Basque.
as a deprecatory term first recorded in a Bugs Bunny cartoon, but a similar noun cotton-picker meaning "contemptible person" dates to around 1919, perhaps with racist overtones that have faded over the years. Before mechanization, cotton picking was the most difficult labor on a plantation.
I drove out to a number of the farms near Denison and found many very young white children working all day in the hot sun picking and dragging sacks of cotton. In one field the labor corps consisted of one woman and six children, one of them 5 years, one 6 years, one 7 years, one 9 years, and two about 11. The father was plowing. The 5 and 6 year olds worked all day as did the rest. The 7-year-old said he picked 50 pounds a day and the 9 year old 75 pounds. (A good picker averages several hundred a day.) School begins late on account of the cotton picking, but the children nearly all prefer school to the picking. Picking hours are long, hot, and deadly monotonous. While the very young children seem to enjoy it, very soon their distaste for it grows into all-absorbing hatred for all work. ["Field Notes of Lewis W. Hine, Child-Labor Conditions in Texas," report to U.S. Congressional Commission on Industrial Relations, 1916]