Reading it in context, I think the best replacement for "a pox on you" (a phrase that I, a native English speaker, have never heard before) would be a simple "darn you". It's forceful enough to show that the speaker is a bit of a bad-mouth, but it's not intense enough to possibly get bleeped out on television.
With my Lego fanfiction, among the ways I've been going for the full spirit of Lego media is by trying to keep the dialogue as kid-friendly as possible. This includes using less intense "near-curses", as I'd like to call them, such as "darn", "heck", "gosh", and "shoot", just to name to ones I can think of off the top of my head right now.
Does this advice help you out a bit?
(Oh, and I guess I would also recommend changing "soppy" to "sappy", if you're trying to show that someone is feeling sad (which I'm assuming, from the context).)