A man joins a very exclusive nudist colony. On his first day there  he
takes off his clothes and starts to wander around. A gorgeous petite
blond walks by, and the man immediately gets an erection.

The Woman  notices his erection, comes over to him and says, 'Did you
call for me?' The  man replies 'No, what do you mean?' She says, 'You
must be new here. Let me  explain. It's a rule here that if you get an
erection it implies you called  for me.' Smiling, she leads him to the
side of the swimming pool, lies down  on a towel, eagerly pulls him to
her and happily lets him have his way with  her.

The man, now  with a contented smile on his face, continues to explore
the colony's  facilities. He enters the Sauna and as he sits down, he
farts. Within  minutes a huge, hairy man lumbers out of the steam room
toward him,
'Did you  call for me?' Says the hairy man.
'No, what do you mean?' says the  newcomer.
'You must be new,' says the hairy man, 'it's a rule that if you  fart, it
implies that you called for me.' The huge man easily spins him  around,
bends him over a bench and has his way with him.

The newcomer  staggers back to the colony office, where he is greeted
by the smiling,  naked receptionist, 'May I help you?' she says. The man
yells, 'Here's my  membership card. You can have the key back and you can
keep the $500 membership  fee.' 'But sir,' she replies, 'you've only been
here for a few hours. You  haven't had the chance to see all our
facilities.'

The man replies,  'Listen lady, I'm 75 years old. I only get an erection
once
a month. I  fart 55 times a day. I'm outta  here!!

The version I heard was the old guy's son put him in  a nursing home. The cute nurses screwed him when he got an erection and the burly orderlies buggered him when he fell down.  The guy calls his son to get him out of there.  He gets an erection once a month but falls down three times a day.