I decided to do some research on the mystery taste that I experience whenever I choose to drink a pilsner or German lager. What I found, while not really great news, certainly explains my previous findings in a reasonable manner.
It turns out that some beer (often in green bottles) uses a yeast strain which produces a sulfur flavor in beer. This is what I dislike. The reason it tasted so much better in a keg is that it is less concentrated. The yeast’s flavors are much more diffused in a keg, and much more intense in a bottle.
It doesn’t mean that beer in a green bottle is bad, though it does have a higher risk of being really skunked (or light-struck). If you want to avoid that, don’t buy beer out on display or in brightly lit coolers. Buy it in a case or 12-pack that is completely sealed. Or, if you are like me and don’t like green bottled beer at all, learn your beer types, and stay away from that style of beer.