Green’s Dictionary of Slang

(Aus.) a completely worthless person.

1999		G. Seal Lingo 128: Related closely to insults are other negative aspects of our informal speech, particularly terms concerned with inefficiency, obsolescence, failure, and uselessness. These include [...] oxygen thief, one who is a waste of space.
2010		D. Mason Marching With the Devil 276: Krapo [...] looked like an overweight and vacuous weasel. Keyman dismissed him an ‘oxygen thief’.