A prostitute goes to the hospital to visit a colleague who is about to
have a heart transplant. She's worried about the friend so she asks the
doctor: Girlfriend: I'm worried about my friend doc, what if her body
rejects the organ?
Doctor: Well she's 36 years old and healthy. How long has she been in
Girlfriend: She's been working since she was 19 years old but what does
that have to do with anything?
Doctor: Well she's been working 17 years and hasn't rejected an organ yet!