「チャックが全開だ」は英語でどう言う？

The other day I arrived at the office after teaching a lesson outside in the morning. I hadn't used the restroom since leaving home, so when I got to the office, I was kind of in a hurry to go to the restroom.

I put down my bag and started walking to the restroom. Thinking ahead, I looked down at my pants, and then I realized it. My fly was down.

• fly チャック (also "zipper")

Since I hadn't been to the restroom since leaving home, it meant my zipper had been open for a few hours. No wonder it was a little bit cooler when I was riding my bicycle! I stopped and snapped this photo before going to the restroom.

• no wonder 驚くに値しない、～も不思議ではない、道理で～なわけだ、無理もない、～も無理はない、なるほど～なわけだ、～も当然である (definition from Eijiro on the Web)

It seems that when I was a kid in Texas, in some cases someone might lean over to you and tell you, "hey, if you don't close the barn doors, the cows are going to get out!"

If you notice someone with their fly down, I recommend that you tell them. They will probably thank you for it. I would have been grateful for someone to have mentioned it to me. In fact, all of you should check your flies now.