"Sisters of Mercy" joke

One very loooooong summer day, not so long ago, a guy was driving down a long and never-ending road, when he noticed a sign that said
Ten miles ahead Sisters of Mercy brothel.
The guy really confused by somewhat intrigued decides that it is weird but if it were true he might check it out.
Later down the road he finds the same sign but it reads five miles ahead the Sisters of Mercy brothel.
So now the guys decides that he is definitely going to stop at the brothel five miles down the road.
FIVE MILES LATER...
He drives into a parking lot in front of a small windowless building with one door that says entrance to the Sisters of Mercy brothel.
He gets up to the door and on the doorknob "Knock three times" is inscribed on it.
So the guy filled with intrigue knocks three times, and immediately after the third knock an extremely old nun opens the door and says.
"Hello, are you looking for a few good nuns."
"Yes, yes I've been on the road all week and I'm pent up like hell, god I am."
As the nun gives the guy a cold look she tells him to come inside and follow the winding path.
So the guy goes through about fifteen hallways and finally comes across a door that says "WAIT"
And after a five minute wait the biggest butch of a nun comes and says high you came for a nun.
After having the shit scared out of him by the big nun she tells him that the nun of his dreams is on the other side of that door, but she tells him he has to strip naked right here and bend over facing the door keeping his eyes closed.
After doing those two tasks he feels the door in front of him swing open, and suddenly a sharp pain in his ass, he was kicked outside and the door slam shut and lock behind him.
As he walked around the long building buck naked, he gets back to the parking lot realizing that his car is missing, and the front door is locked. As he turns around he notices a card on the ground and opens it up and he reads
! CONGRATULATIONS YOU HAVE BEEN SCREWED BY THE SISTERS OF MERCY!