A play on Soda Jerk . Comes from the situation that most Coffee House attendants are in: usually young, no social life, bored with life and only work there for the free Italian Sodas and Biscotti; Just like the stereotypical 1950's teenager who worked at the local diner after school.
And the more sinister meaning, a sort of corallary to Coffee Nazi, is the counter clerk who mocks all patrons who do not order what he believes to be the One true Brew -- "You want whipped cream on that? Whipped cream! I got your whipped cream right HERE! HERE'S YOUR WHIPPED CREAM! **WHAM**".