'DON'T DROP!'

I was just coming back from the grocers before, with stuff for tea, and as I came into the laneway there were two guys coming out, one who I recognised from hanging out with at Flinders Street steps a few nights ago, and another guy who I didn't recognise.
As I passed them, the guy who I didn't recognise yelled out, 'OI!' I stopped and turned around to look at them, and he yelled, 'DON'T DROP!'
I said, 'What?'
He said, 'DON'T O.D.!'
So he must've thought I was there to inject heroin, and that I was going to do it on my own - which is a really bad idea, because then there's no-one to get help if you overdose.