According to Plies, "Becky" is referring to the act of fellatio. Plies terms the act "Becky" because of the widely held notion and/or stereotype that Caucasian women are somewhat more sexually liberal in terms of frequency of encounters, random partnering, and overall lasciviousness. With "Becky" being a popular name given to females at birth in the White society, one can assume that Plies simply chose this name because of its unique association to "Whiteness", particularly where the female is concerned.
