First of all, if you don't know what a "dupe" is, it's short for duplicate. It's another word for a product that is similar to another product.
If you remember OPI's Katy Perry collection, you probably remember the Teenage Dream polish. Teenage dream is a pink glitter in a clear base. Some of the glitters are larger than others and those glitters reflect rainbow colors. Because Teenage Dream was limited edition and so sought after, you may have missed out on it. I stumbled upon a display of the new Maybelline Color Show Sequin polishes today at Rite-Aid and instantly thought that one of the colors, Rose Bling, looked extremely similar to Teenage Dream.
Overall, if you are kicking yourself for not buying the Teenage Dream polish when it came out, instead of buying it for more than it's worth on the internet, I think that the Maybelline polish would be a very good product to buy to replicate Teenage Dream. The Maybelline polish has all of the pretty details that the OPI polish has, such as the rainbow reflections, the different sized glitters, and with just one coat of each polish, it gives about the same amount of glitter onto the nail. The only differences are that the Maybelline glitters are a couple of shades darker, and the large glitters in the Maybelline polish are bigger than the darker colors in the OPI polish. If you are still on the hunt for Teenage Dream, I definitely reccomend checking out Rose Bling Sequin polish from the Maybelline Color Show line.