Came out of my office yesterday, unlocked my bike, and got pretty much across the street before noticing my back tire was sounding odd.
(I've recently been using a water bottle that's a little smaller and noisier than my usual, so it took me a moment to catch on that that wasn't where the rattling was coming from.)
Pulled up, realized my rear tire--the tube in which is just a month or so old--was entirely flat. Flipped it over, and discovered the tube folded over...
Either I am the world's biggest moron at tube installation--yet it lasted like this for weeks--or someone came by sometime during the day and, frustrated that they couldn't steal the bike or even its front wheel, instead deflated the tube, took the rear wheel off, took the tube out, folded it in half and stuck it back in the tire, then put the tire back on the wheel just well enough to be convincing and put the wheel back on the bike.
Perhaps I'm extra pissed because I was already having a bad week, and I not only missed meeting up with my Friend but missed Sara Watkins' performance at TRAF and half of trivia---some part of the back of my mind can see how this could almost be a prank if I were in a much better mood---but who the fuck does shit like this?
(And, of course, although I managed to ride from TRAF to the North Side, and thence to Lawrenceville, last night, this morning the tire was halfway to flat again--and, of course, I didn't have time to figure out why. Fortunately I already have a spare tube in stock...)
This week's lesson: In Oakland, lock your frame and both your wheels.
...and ride a cheap bike.
I do not suspect foul play. My hunch is that the flat happened on its own, while you were in the office. The fold-over occurred just in the short ride across the street.
You step on the pedal, applying power, which is transmitted through the chain to the wheel. The wheel, if not physically stuck to the tire adhesively, can turn inside the tire, taking the tube with it. That can result in the tube fold you describe.
haha, i couldn't figure out what happened when i first read that but i think stu has it...
this is the same tire that went flat on ARB a few weeks ago? maybe we missed some debris in the tire?
Well thank you, Stu, you've assuaged my anger, if not my annoyance...
(there does turn out to be a pinhole in the tube--approximately across from the valve--which I am apparently no good at patching, which both supports your theory and does nothing at all for my irritation level...)
Salty, same tire, new tube. I've been over with my fingers a couple times, though, and while I'm not certain, I think it's in a different place...
This hole is on a seam--maybe I just over-inflated it just enough?
That first flat (on ARB) was a pinch flat so make sure the rim doesnt have a sharp burr from where it hit the rock or watever.
I had a flat two weeks ago that turned out to be a piece of wire from the tire bead sticking out, so check that too since that would be consistent with a pinch.
Gremlins.
HA! That works, too 
(This week's lesson turns out to actually be an oldie but goodie: Never assume malice in anything incompetence will explain. Especially if it's your own.)
@ B.B. Sara Watkins' performance at TRAF
She's a great musician, but it was a really sucky venue for an acoustic duo.
