The intended answer is "grandfather paradox". The joke is that a non-scientific response is given.It would be very mean and sad.Because the poor guy would be homeless.And he would be ultimate ungrateful bastard.
What do you call it when someone goes back in time and kills their grandfather? Mean.
That's too harsh a term. We must not hurt people's feelings.Or murder.
RMT
That's too harsh a term. We must not hurt people's feelings.