Ex-“Saturday Night Live” funnyfella-turned-movie-star JASON SUDEIKIS took a nasty tumble when he got all macho on a motorcycle during filming of his new flick “Tumbledown” in snowy Princeton, Massachusetts!

Waiting to film a motorcycle sequence, Jason jumped on the bike with a cocky grin and proceeded to show cast and crew he’s a Wild One – racing it up and down the snow-lined streets, even popping an eye-popping wheelie as everyone gasped, until… Sssliiiide! – his wheels slid over a patch of black ice and he instantly lost control!

The bike fishtailed, slammed into a curb and sent Jason flying – but here’s the good news: He landed in a snowbank! As everyone rushed up, the dazed star mumbled: “HOLY S***!…What the hell just happened?”

After being helped up, humbled Jason told the director it might be better to let a stuntman double for him in the motorcycle scene. Co-star REBECCA HALL seconded that emotion, saying that even though the script called for her to ride double behind Jason, she was suddenly too damn scared to ride a murdercycle!

Ironically, the director had wanted to use stunt doubles for the scene – until Jason said he’d do it himself and started demonstrating what a real cool tool he was aboard a bike!