North Tower Doctor

Alright listen up, chucklenuts. This joke is playing on two things: 1. The North and South Towers being involved in the September 11 attacks and 2. CPR (cardiopulmonary resuscitation) which is, like, what doctors do to save people when they are dying and stuff. The joke is saying that the North Tower was a bad doctor because it didn't perform CPR on the South Tower when it collapsed. You probably didn't even know September 11 was a real day. No wonder your mom is sad all the time.