By 'lowest of the low' I mean that the person using the substance must be really down-bad and desperate, so badly to the point where they are willing to do literally ANYTHING to get high, even if the high is very short-lived and (more often than not) very shitty and has the potential to leave you with severe brain-damage or even kill you after one use. So which inhalant do you think embodies that the most?
In my opinion, it would be huffing Freon from AC units, weather you're siphoning it from the unit in a bag or you are huffing it directly. Either that, or huffing gasoline out the can.