If I’m wearing a butt plug on an airplane is there danger of it popping out due to the pressure changes?
No. The only way I could possibly see something like this being a danger would be if the butt plug was unbelievably large and your ass was unbelievably tight. Otherwise, your ass is stretchy enough that any air will slowly seep out, like a slow fart.
Obviously you are going to want to avoid any metal toys, whether cock rings or butt plugs. It’s just not worth the hassle or investigation when going through security. And if you’re having hot airport security fantasies, I don’t think they’ll get fulfilled the way you want them.