Adam: i don't think this is correct answer
jack: you suck at math lol
Adam: wow! i was writing and publishing my research articles when you were in your dad's lumbar, kiddo
"your mom is your dad's mom" is a satirical reference to jokes beginning with "your mom is..."
it came from boredom while walking around target.
if someone is telling "your mom..." jokes, tell them this one, and you will win, for sure, i promise. they won't know what to say. guaranteed to work, everytime.