Embarrassing Zipper Down Moment!

So I went to the store and I used the bathroom when i got there first. I shopped and then when I went to pay the cashier was giggling and shaking her head and when I looked down I realized it. I left my zipper down and it had worked itself wide open!!!! Also the boxers had become open as well so part of my thing was visible! I zipped up and said I'm so sorry and the lady was just laughing. I paid and left real quick!!