It could be worse. Could have stomped you after

Giddyup??

I suppose your horse couldn't take all the pressure.

animals do have a way when it comes to doing the wrong things at the wrong time. I'm guessing your horse has that skill

A client?

When you felt embarrassed, your consternation wavered and the horse sensed it. Stay focused and confident. :)

Tell it to stop horsing around!

I think one thing all equestrians can agree on is that random things can and will happen, especially at shows where everyone is stressed and excited. I'm sure a simple explanation of what happened will be enough for your client, as these things do happen, and (usually) aren't an indicator of your training abilities. I hope you and your horse are uninjured, and wish you luck at future rodeos!

Your horse was like, "A good trainer, eh? Haha, not today, pal."

yeah sure.