J.O.... I don't have an aunt Sally so I'm not sure what you mean.
Just think of it as a 'dig' along the lines that "maybe the solution reached was logically flawed".
Comes from a maths mnemonic "Please Excuse My Dear Aunt Sally"; Parentheses, Exponents, Multiplication, Division, Addition (and) Subtraction.
Put another way, it could be said that those who remember it have been around too long!