Everyone hopes they have an original costume when they dress up for Halloween -- but this year, a lot of celebs dressed up in eerily similar ensembles.

Hard to believe, but both Rihanna and Lady Gaga dressed up in marijuana-themed costumes for their respective Halloween parties last night ... Rihanna in West Hollywood and Gaga in Puerto Rico.

While RiRi kept it sexy with a green lace gown and veil, Gaga put almost everything on display ... covering up her nipples with giant marijuana leaf pasties.

"BEST COSTUME EVER ITS SO FUN. Princess High the Cannabis Queen," Gaga tweeted earlier this morning.

But was is the "BEST COSTUME EVER" ... or do you prefer Rihanna's version of Mary Jane? Vote below:

They weren't the only celebs with Halloween twins out there this year though. Check out all the other doubles below ... and vote for the better look!

Kim Kardashian and Ivanka Trump were copycats this week ... both dressing up as different versions of Catwoman.

While Kim did Michelle Pfeiffer's stitched together catsuit, Trump's is more Julie Newmar.

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At the same party, Kim's sister Kourtney and her baby daddy Scott Disick dressed as two other Batman characters: Batgirl and Robin.

But swap the gender roles, and you've got Paris Hilton and boyfriend River Viiperi's costumes.

Kim's mom also had a double out there, as both Kris Jenner and "Chelsea Lately" star Heather McDonald dressed as Wonder Woman.

We gotta give props to Heather for actually wearing one that fits ... unlike Kris, who had a double nip slip in her too-small costume.

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Neil Patrick Harris and Adam Lambert took on two very different interpretations of the Hollywood vampire ... both sporting fangs and white contact lenses.

But while NPH gets points for going shirtless, Adam dressed his up a bit ... and added some killer makeup and long white hair.

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Geek chic was in for Calista Flockhart and Jwoww, who both dressed as nerds for their respective Halloween parties.

But who looks better rocking a pocket protector?

We're actually surprised we didn't see more of this one this year -- Miranda Lambert and Kevin Farley were the only two Honey Boo Boos we could find!

Miranda nailed it and Kevin looked pretty hilarious, we just wish they had accessorized with some Go-Go juice or a pet Glitzy too.

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Purple reigned this year too, as both "90210" star Matt Lanter and Diddy rocked some crushed velvet to dress as Prince.

Diddy's girlfriend, Cassie, had a double too!

Both Gisele Bundchen and the R&B singer paid homage to Elizabeth Taylor's version of Cleopatra this year, sporting almost identical makeup.

And, last but not least, we had two women going under the sea as sexy sirens.

Kim Kardashian and "Basketball Wives" star Evelyn Lozada both dressed as mermaids -- with Kim going as Daryl Hannah's "Madison" from "Splash" and Evelyn filling her clamshell bra as Ariel.

And check out even more celebrity Halloween costumes below!


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