The actor attended one of Swift's three shows at NOLA's Caesars Superdome.
The rockers parodied a 'Deadpool' teaser from 2018.
He also shouted out Justin Timberlake, who wasn't in attendance.
The movie, also starring Hugh Jackman, opens in theaters on July 26.
Stray Kids are also contributing an original song titled "Slash" to the upcoming Marvel film, Deadpool & Wolverine
Reynolds and McElhenney dressed up as George Michael and Andrew Ridgeley, respectively.
"I feel like I should remember this," the actor captioned the hilarious image.
The A-lister and wife Blake Lively are currently expecting another child of their own.
