Rap God is a Watch floor where the player can explore a trashed, secluded floor of an apartment building and talk to one of the five interactable people.
The five people you can talk to each have their own limited dialogue. For example, according to one of them (the purple shirt), there are 24 people as a group, but due to an "unexplained attack" (the brown shirt) and "mysterious disappearances", they are down to 5 people remaining.
You can see how well-armed they are when you visit the room with the black shirt, and obviously while you try to ask for a weapon, he'll simply refuse.
Trivia
The floor was inspired by a map called ph_apartments in the Garry's Mod Steam workshop. It was supposed to be the whole map, but it would have taken too long to develop and too much time to get to the next floor according to one of its floor developers (not one of the main developers).