Costello: I've been experimenting with shortwaves!It's a joke so clean you could tell your grandparents! And for those people who AREN'T grandparents, here's some context: a WAVE, a WAC, and for additional bonus points, a WREN.
Abbott: When did you start experimenting with shortwaves?
Costello: Ever since I got slapped by a tall WAC!
PS: Overheard on the March 7, 1946 edition of the "Abbott and Costello Show."