I've a few contenders in my old Game Color set - to be fair to Vallejo I think the case of paint had probably be sat around at the game store for a long time. Still some of them were so separated and thick they have proved impossible to get back to any reasonable consistency.
In the category of just crud was their orange - which is so rubbish even the label has rubbed off so I can't tell you exactly what it was called. However one advantage of the re-formulation of the range is the current "hot orange" is actually rather nice and perfectly capable of covering things evenly, my old one is just all over the place. Still won't totally forgive them for getting rid of a few favourite colours however!
I've had some woe with the first version of the Army Painter speed paints and having them reactivate under various circumstances, but to be fair to them I understand this is fixed in their v2 range.
