Madonna to Diplo -- Don't Fall for the Banana in the Tailpipe (VIDEO)

Madonna surprised her opening night crowd by bringing Diplo on stage -- and then super surprised Diplo by making him bend over and accept a banana.

That's pretty much what happened Wednesday night in Montreal ... where Madge kicked off her "Rebel Heart" tour. Diplo seemed shocked he was expected to bust out dance moves -- but his parting gift was what really got his attention.