look up any word, like blumpkin:
 
1.
fanny is a euphemism for the buttocks. So the exclamation "My Aunt Fanny!" or "My great Aunt Fanny!" is to say
"My ass!" as something of a perturbed rebuttal or reply
"I think YOU dented my car."

(surprise and denial) "My great Aunt Fanny! I did not!"
by theguywhobrokethebank November 01, 2013
1 0