Let me think... I have returned an eyeshadow, a Fluidline, Strobe Cream, and a Nail Lacquer. My mother returned Prep + Prime Eye. The eyeshadow was a gift for my birthday, and it was Contrast, a dark blue-purple, that showed up a really muddy purple that I disliked and exchanged for Deep Truth. The Fluidline was Haunting, again for my b-day, and it's this light white-ish purple. It's pretty but so not me, exchanged for Blacktrack. The Strobe Cream made me break out SO bad that I almost cried, returned for Fertile and #7 lashes. The Nail Lacquer was a few years ago and it was I think the 3rd MAC item I purchased. I bought it in the city at Henri Bendell. When I got home, it was dried up. ;-; The next month we returned and I got it exchanged for a not dried up Kid Orange. =D A few months later I got a MAC closer to me and my life became a sparkling blur of makeup and MAC.
Today I'm going to exchange Parfait Amour for Carbon. It seems like I've returned a lot, but seriously I keep so so so so so much more than I return.