There was this boy in high school that was what you would
consider a nerd. Anyway he had his own lab in the basement
of his home and one night he came up and said "Dad look
what I made." So he poured a flask of fluid into a pot of
soil and instantly grass started to grow.

Of course his dad was really impressed with this and asked
his son if he can make something to make his penis grow.

His son thought for a minute and said that if he did then
dad would have to buy him a convertable.

Dad agreed. 

The next night the son came out of the basement and gave his
dad a vial. The next morning his father came to him and told
him that he had something to show him. They went to the front
yard and the boy saw a cherry red ferrari.

The son looked at his dad and said "I only asked for a convertable."

The dad replied "the convertable is in the garage. The Ferrari is
from your mother."