Color (http://en.wikipedia.org/wiki/Color_Labs). The idea behind the app was flawed (as in "why would anyone need this?"), and they made no attempt to hide the fact that the underlying idea was datamining/advertisement.
I don't think Color is a terrible idea. The concept of group photo collaboration, where many people who don't know each other can contribute to the same photo album (i.e. during an event/etc) isn't that bad. Their execution for the ludicrous amount of money they raised was most definitely embarrassing though.