"Uncle - I can explain."
"No need to explain Timmy - you're a sissy who loves wearing girlie clothes. No shame in that - you look very pretty. So this deal is this - you get to cum, but I get to fuck your ass and Auntie Jane films the whole thing. We might all make some good money - 3-ways."
"Now If your cock is hard right now, I'll take that as a yes."
"But Uncle no!"
"That looks like a yes to me."