That’s somewhat true. Your tissue oxidizes from contact with air. That’s what the “antioxidants” you hear about are. Oxygen enters the cells and most goes to the Meme powerhouse- the mitochondria. A small percent escapes into the cell, and just like metal rusts- the oxygen damages the tissues of the cell or even the DNA. This damage can cause reduced performance of the cell. But if the DNA is damaged- when time comes for the cell to replicate a new replacement, the replacement will come out damaged, and that damage can be magnified each time the cell copies and even lead to cancer. If you stop breathing you’ll have more immediate problems though. So oxygen is slowly contributing to cell damage and ultimately death- but don’t sweat it. It takes awhile.
Your comments typically make me think rather than laugh, but this one is definitely an exception