Dear Twilight Sparkle:
I see. You plan on getting some at the Gala.
I wonder...
Oh, nothing. Nothing at all.
We ponies hardly ever wear clothes, true. So, given that we ponies are waving our plots out for all to see, you'd think that we would always feel horny. Of course, because you're a unicorn, you're always horny. And for that matter, your brother and foalsitter are also always horny. You wouldn't believe how much sex it takes for them to be satisfied.
Now that I've hopefully managed to traumatize you for life, let's talk about your dresses. If you've forgotten what sexiness is all about, then all the slutty dresses in the world aren't going to get you laid. But then again, I suppose that's what you get for living in a town of inbred hicks.
Regardless, if you've managed to convince Hoity Toity to buy into your attempts at getting laid, then I'd say you can't fail.
Nope. You're going to do just fine.
Your equally "horny" former teacher, Princess Celestia.