This expression has always struck me as really odd from the start. It alerted me to the possibility that those claiming knowledge of physics weren't perhaps as able to work with those laws in practice as they thought.
I was always way to intimidated to continue that thought. As time has gone on, I've been able to put my doubts into words.
The laws of physics describe how the universe works. It is reality. How can you defy that? Either you'll find something else you didn't know before you add to science, or you will be in big trouble. But you cannot 'defy' the laws of how things really work.
Sounds much more like the law of the land or even accepted morality. That kind of shows how physics is being invoked, as something to browbeat and intimidate, you are breaking the rules of what is accepted and that's really annoying. It's an attempt to silence others and continue not listening to what's actually being said.
Defying your interpretation of the laws of physics is more like it and its the body that does that.