A few weeks ago, I bought my first bottle of Umeboshi Plum Vinegar.  I bought it a my local HFS.  It is a smallish, brown glass bottle with a shaker top.  I tried the UPV and immediately fell in love with it.  I started putting it on everything.

I have kept it in my pantry as I do all vinegars.  I didn't use it for about a week, and when I went to use it yesterday on some Talapia, I got a distinctively funky taste from it.  Sort of reminded me of dirty socks.

Can UPV go bad?  Should it be stored in the fridge?  I took a look at the bottle and didn't notice anything about specific storage.

I think I'm going to throw this bottle out and start fresh, but I've only had it a couple of weeks, and have used only the tiniest bit.  I would hate to think that it is that perishable.  And, no, my house isn't warm (in fact, often too chilly for some family members), nor was it exposed to any significant heat.

What gives?

I don't know about what you have, but Eden Ume Plum Vinegar keeps for a long time at room temp without changing taste.  Long time, like a year or two ..

Don't throw it out- bring it back to the store where you bought it. Ume vinegar should NOT go bad after only a few weeks. I've had an opened  bottle (forgotten about) in the back of my pantry for a year, and it was still fine. If it went bad that quickly, it may have been "past its prime- about to turn" when you first bought it.

you should have kept it in the fridge once opened

My bottle says to store in fridge once opened.