"wearing black jeans and a black T-shirt ... straps visible on my torso, a complicated device hanging off my belt, was walking with a long and confident stride and jingling faintly as I went"

I stand by "ninja". Or possibly, "death" :)

But ninjas are masters of stealth! They certainly wouldn't jingle, and I doubt they'd go in for intimidating people on the street either. If you see a ninja and survive, the ninja will probably get a poor rating at their next performance review :-)

If death is an amiable ginger computer programmer I'm very, *very* disturbed.

Jim Bloggs?
"Huh? What happened – oh. Hang on, this can't be right. I'm sure I shouldn't be dead!"
Shouldn't you? What were you doing when it happened?
"Well, yesterday I ate some funny-tasting salmon mousse ..."
Not from a tin branded "Dibbler Tinned Fish Co.", by any chance?
"Yes, actually. Anyway, I had a bit of a stomach ache today and was feeling a bit off, then next thing I know I'm all transparent and my body is lying around my feet."
Ah, yes. I'm afraid that's a known bug.

Oh well played...