His friend says, "My feet are cold mate. Can you go and get me my slippers from upstairs please."
The guy goes upstairs, and there are his mate's gorgeous twin 18 year old daughters.
"Hi, girls. Your dad sent me up here to shag you."
The first daughter says, "That's not true."
He says, "I'll prove it."
He yells down the stairs, "Both of them?"
His mate yells back, "Of course, both of them."