There was a family gathering, with all generations around the table .....
Mischievous teenagers put a Viagra tablet into Grandpa's drink, and after a while, Grandpa excused himself because he had to go to the bathroom .
When he returned , however, his trousers are wet all over .
'What happened, Grandpa?' asked his concerned children.
'Well,' he answered, 'I don't really know.
I had to go to the bathroom ; so , I took it out and started to pee , but then, I saw that it wasn't mine, so I put it back !'