I found someone who worked there and told him what happened. This guy had actually been stocking the freezer beside me when it happened. I was very polite, very calm, and explained that it was important to me because it was the only thing that was given to me when my grandmother passed away. I asked if there was anything that could be done to get it out.
Now, I could understand if there wasn't anything he could do, but I don't think this was the right way to go about it:
Him: Oh, is it a diamond?
Him: Well that's too bad then.
He was so cocky when he said it, and then he just walked away. UH WHAT? By then I started to get really upset. I didn't yell at anyone, but I was definitely crying. I went to a cashier hoping to get a manager, but after expressing her own, "Oh that sucks" she told me that he wasn't in and there probably wasn't anything he could do anyway. :/
Even if there wasn't anything that they could do, I just feel like they were really rude about the whole thing.
ETA I accidentally typed 'Costco' at first. Whoops.
ETA again I guess I should be more clear about his tone when he said it was too bad. Think of the way you'd say, "Ha, that sucks for you!" and that's pretty much it. I don't blame the store for my lost earring, I wasn't sticking around for coupons or anything, I just honestly wanted to know if there was anything that could be done about getting my earring out.