Yep I totally agree, it's really only on the inhale I can detect it. Kind of a short, sharp off flavor that goes away quickly. I'm a craft beer lover, and drink a lot of sour beers, which generally use lactobacillus and/or brettanomyces to produce the sour flavors. In some of the very strong sour beers there is sometimes a vinegar-like flavor that comes though. That flavor is what I am reminded of when I detect that "funk" similar to apple cider vinegar. That flavor is delicious (when in balance) in beer, in juice I don't know, but it reminds me of tasty beer enough that I don't find it offensive, so maybe that's why I detect the funk less than you.
I would prefer if it wasn't there though obviously. I'd imagine our samples were the same mix (80/20 pg/vg and 12mg nic with zero shots) so I don't think the ratios would have caused a more pronounced or a more subdued flavor. It could just be different personal tastes and all that jazz too I guess.
It's odd because I've tasted a similar flavor in other apple juices. I think it was Madvape's Top Vapor apple pie or apple cider or something that tasted a bit like MBV's red apple as far as the funky taste (although red apple is far better overall and has far less of that funky flavor) It must be something in a certain flavoring agent that causes it, most all the apple juices I've tried (which is a lot, I was on an apple kick awhile ago) either taste like apple jolly ranchers or they taste like fresh apples but have some sort of little off flavor. Maybe fresh apple flavor is just impossible to translate into an extract or flavoring without producing some off flavors.
Something else I just thought of, apple cider vinegar is made from fermenting alcoholic apple cider (converts alcohol into acids) Maybe the apple flavoring used is an actual alcohol based extract or something, and there is a slight bit of fermentation that goes on and produces those acids. Or maybe they add the acids to mimic the flavor of apples. I don't know. I'm sure it's something acid related or alcohol related though