The actor, 42, posted a snap of himself wearing an ornate Christmas jumper, alongside Jake Gyllenhall and Hugh Jackman.
They said “it was a sweater party”, he wrote.
His A-List friends looked as though they could not stop laughing, while Reynolds kept a straight face, at what looked like a festive party.
The Green Lantern and Deadpool star, who is married to Blake Lively, is known for his funny Instagram posts.
Recent posts include a quip about meeting Sir Paul McCartney.
Reynolds shared a picture on himself with the Beatles star – and joked that it was probably a lifetime highlight for Sir Paul.
“Have you ever had a dream to meet someone so badly and somehow it comes true?
“You’re welcome, Paul,” he wrote.