From slanglang.net,
“What's the origin of Tallywacker?
The origin of the term is uncertain but first half can come from the 15th century english where ‘tally’ meant a stick with notches, or can come from the latin word “talea” meaning stick or rod.
There is also an alternative etymology for the word “Tallywacker”, which is that the word ‘tail’ was used as a slang between the 17C-18C.
Given this information, it can quite possibly be that this urban slang formed itself throughout the years.”
My tallywacker works best when there is a connection that transcends the tally and the wacker.
Anonymous: "You're only as old as the girl (or boy) that you feel."