Technically, you don't breathe oxygen, you breathe air, a gaseous mixture composed of roughly (by molar content or volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor ...
... *takes of spectacles ... breathes fog on the lenses and wipes them with my bow-tie. Rubs the bridge of my nose and puts them back on*
... then again, this is depends on ones definition of "breathe" as referring to the respiratory process during which said components of the gaseous mixture are sequestered in the lungs and oxygen, being essential for aerobic metabolism, is transported in the blood plasma via haemogl ...