To make his father unable to get hard

When their parents arrive they seem to have been shopping
When he sees them he smiles
"Stop both of you!" you order and they stop in the place, still with the bags in her hands
He smiles seeing their scared look
"Don't worry everything will go fine"
Then he looks at his father "daddy you always hated me... so it's **** time"
"From now on, each time you try to have sex, you'll be unable, your cock will get reduced to it's minimal size, as if it was in very cold water. You'll need sex more and more, but you'll be unable to use your cock for it"
Then he's an idea and smiles "the only way you'll get hard, is by having a man fucking your ass"
He points at the kitchen "Now, forget this talk, and get the things you bought in place. You can't hear whatever we do here"
As he does, you look at your mother with lust