What do I need a "Show Shirt" for?

OK, here's the deal, first, Yes I'm still hogging the bandwidth space, hey, there are TWO of the femme fetal types to my one macho gelding type!

So anyway, today my human comes into the barn in a happy mood. Now I like it when she's in a happy mood because she usually tells me I'm extra cute and doesn't make me work too hard. But today it was kind of weird... She brought in a human shirt and made ME 'wear' it by hanging it off of my saddle...

Now, first, I am a BOY, I am NOT so thrilled to have some frilly, jeweled shirt near me, let alone ON me and secondly, what does she mean when she says this is a 'show' shirt? What the heck is a show? She keeps chattering about how we're going to start 'showing' this spring... What does this mean and why does she need a shirt that looks good with me and my Western Show Saddle to do it in?

Women, no matter if they're human or equid, they're confusing to a cool dude like me.

Peace out dudes!