Oxygen is a nasty habit that humans have.
From Scrubs Season 2 Episode 6 "My Big Brother"
DR. COX (to TURK): Hey, Ghandi. For your information, I attended that poor vegetable's funeral every single time I set foot in his room over the last six weeks. Thank God the family finally moved him over to Surgery, where you guys were good enough to help him kick that nasty oxygen habit he had once and for all.