Someone who doesn't deserve the air that they breathe. An incompetent. Usually overweight or useless. Usually talks a load of shite.
So reads the usual references of the term. Unfortunately most of the planet could fall under that description. Admittedly some people like RMPs and RAF Police are born into that category but who is to judge that anybody be reduced to the status of Oxygen Thief? I suggest that a few ground rules be established.
Pavarotti was overweight but he could croon a good melody. He was also worth a packet. If everyone who talked shite was reduced to Oxygen Thief then all of the Houses of Parliament would be similarly condemned. All Subalterns, Midshipmen and Pilot Officers would also be tarred with the same brush along with Local Government Officers, Health and Safety officials and Time Share salesmen. Hell! Let's just kill 'em all!