Most Mac foundations, with the exception of the original formulation of Hyperreal, which I do love. All the others have broken/irritated my skin like there's no tomorrow and I'm nowhere near being a teenager. I'm not even tempted to try new MAC foundations anymore.
Also shadesticks - not loving any product that requires me to scrub my delicate eyelid area just to apply it. I'll stick to paints and other easier to apply products.
Oh and those CCBs. Pretty much a useless product. I prefer creme to powder products any day.
The spray blushes, those showed up at my CCO en mass. Great idea, poor execution.
Metal-X cream eyeshadows. Who doesn't want eyeshadows with built in creasing?
There's more, that's all I can think of at the moment. Not all of Mac's products are winners.