early on in my Mac days I would buy everything that I would see people saying "OMG you must have this, its great" so my collection is pretty large now with things that I rarely wear because they just didn't fit me.
Lipgellies- WHY!!!!!! I didn't expect the coverage of a lipglass or lipstick but damn its like nothing is on at all. I got them when C-Shock came out and EVE I think had them in her video "Tambourine". To tell the truth I still use goldensoft over certain lipsticks, but give it 15 minutes and its gone.
Peticoat - When people said "it enlarges pores" a light bulb in my head went off. Its like I tried to work with it, but something was always off.
Passionate Eyeshadow - I dont know if I got a bad one (the label came off like in two days of owning it, and yes I got it from the mac website) but for such a bright shadow the color pay off even with a base wasn't what I was expecting. Then, it just dried out and hardened. I ended up scratching the shadow out and using it for B2M.
Mineralize Satinfinish Foundation - A ghostly horror in a bottle. Im an NC 50 and it looked like a pale white mess on me. That got B2M'd with the quickness.