“Hangover” star and stand-up comic Zach Galifianakis was a stand-up guy, literally, when he was asked to come pitch in and help at a New York comedy club Wednesday night. “Zach used to work at my club Stand Up NY as a night manager,” club owner Dani Zoldan posted on Facebook. “I tweeted him as a joke asking him if he can come in . . . to fill a shift as a night manager.” And lo and behold, “he came in!” Spies at the Upper West Side club said that the burly comic actor arrived alone, and “spent some time at the bar, then stood in the back watching the show,” which included Greg Warren, Joe List and Ryan Reiss. “No one bothered him, let alone realized it was him.” The club’s managers then asked Galifianakis if he’d like to take the stage himself, but he declined to be in the spotlight. “He said the club looked better than when he used to work there,” a spy cracked. “He hadn’t been to the club in at least four-plus years.” The actor’s been in town promoting his third “Hangover” movie with Bradley Cooper and Ed Helms. He had an early wake -up call to appear on “Today” yesterday, where he was interviewed then also crashed a Martha Stewart segment.