"Transplant" joke

There was a guy who had been having chronic trouble in trying to get an erection.
After weeks of frustration, he finally breaks down and and goes to the doctor. The
doctor gives him a thorough examination and finally makes the diagnosis.
"Well, there's good news and there's bad news," she says. "The bad news is that the
muscles around your penis are deteriorating, and there is no cure."
The guy, on the verge of panic, finally regains his composure.
"So what's the good news?" he asks.
The doctor says, "There is an experimental treatment available, but there are no
guarantees. It involves transplanting the muscles from a baby elephant's trunk into
your penis. Would you like to try it?"
The guy thinks about it and finally says, "Well, the thought of going through life
without being able to have sex is just too much for me. What have I got to lose? Let's
do it."
So the doctor performs the operation.
A few weeks later, the guy takes his girlfriend out to a nice restaurant to celebrate
his new equipment. While sitting at the table, he feels a stirring between his legs; it
gets progressively worse until it reaches the point of being painful.
Seeking relief, he reaches down and unzips his fly to relieve some of the pressure.
Suddenly, his penis leaps free from his pants, slides over the tabletop and grabs a
dinner roll, then returns to his pants again.
"Wow!" says his stunned girlfriend, "That was impressive! Can you do that again?"
Eyes watering and face flushed, he says, "Probably... But I don't know if I can fit
another dinner roll up my ass!"