Tube on the front of my commuting bike. As I'd recently changed the tyres, I assumed that I must have done something to the tube. A long cut, on the side facing the rim. Very weird. Patched in a couple of places, but the first patch exploded when I pumped the tyre back up.
I took that off, and put another (slightly smaller) patch one. That seemed to hold, but after 5 minutes the tyre was flat again. When I examined the tube again the cut had extended out from under the patch. That tube was no good, into the bin it went.
Last spare tube now in the tyre, I hope it holds and it's not something on the rim that was causing the problem. I ran my fingers along it, but it seemed ok.