It’s good to see Vince Vaughn back riding that Red Bull. He’s lost the “fat and happy” look. The caffeine is back, and so is the breathless manic patter.

In “The Watch,” the neighborhood-watch-discovers-an-alien-invasion comedy, he’s second banana to Ben Stiller, trying like heck to keep from being third-billed to Jonah Hill. So he’s back to his old self, riffing like a fiend, improvising nicknames for the other characters — “Franklin” (Hill) becomes “Frank-n-Beans,” “Frank-n-Furter,” Evan (Stiller) is “Evan-rude,” “Evander,” “Ever-ready.”

Vaughn’s brought his A-game to a sometimes ponderous, sometimes explosively funny comedy that benefits from a “Top THIS” one-liner ethos from the cast. Stiller does a variation of his overly-earnest straight-man shtick — Evan is a Glenview, Ohio Costco manager who obsessively exercises, obsessively collects “friends” of every race and creed, who obsessively organizes “clubs.” Bob (Vaughn) joins Evan’s Neighborhood Watch to get out of the house, away from the wife and kid, drink Budweiser and lead BTO sing-alongs.

Hill’s Franklin has an oily Lee Harvey Oswald haircut, a thing for military surplus clothes and switchblades, and is totally down with “this vigilante squad, militia, whatever you’re calling it.”

And Jamarcas (Richard Ayoade of British TV’s “The IT Crowd”) is the frizzy-haired foreigner who just wants to assimilate. A bit.

The screenwriters (Seth Rogen among them) took inspiration from the paranoid “Twilight Zone” episode, “The Monsters are Due on Maple Street” and the screen comedy “The Burbs” in trying to cook up some reason to get these guys together, talking dirty, swilling beer and increasingly paranoid at the bizarre murders that are popping up in their quiet suburb. Something with green goo and tentacles is skinning people. And it may be disguising itself as one of them — a neighbor, the boy going a little too far with Bob’s teenage daughter, the doofus cop (Will Forte).

The plot is secondary here, an excuse to put the foursome in a soccer-mom-mobile, drinking and topping each other’s jokes about urinating in a beer can and “share” — their disappointments at not joining the police force, at not being attractive to women, at Facebook stalking their sexually curious teenage daughter. Vaughn’s been playing dads lately, and he makes those shouted scenes with Chelsea (Erin Moriarty) sing.

“You’re gonna let some guy car wash the inside of your mouth with his tongue? On FACEBOOK?”

The bits are funnier than the movie that Rogen, co-writer Evan Goldberg (“Pineapple Express”) and director and “Saturday Night Live” vet Akiva Schaffer (“Hot Rod”) cook up around them. R. Lee Ermey shows up to cuss, call the watchers girly names and wave a shotgun around. There’s an orgy, so look for “SNL” cameos in that.

And Rosemarie DeWitt, who broke out with “Mad Men,” does the sexually voracious thing as Evan’s hot-to-get-preggers wife.

The graphic violence — played for gooey laughs — and the flat-footed way the movie stops any time a special effect (there are aliens, after all) is needed cripple “The Watch.” The post-Trayvon Martin subject matter doesn’t have quite the bad timing of “Step Up: Revolution,” which has dance scenes with smoke bombs and gas masks that take us to Aurora, Colorado.

But if we can’t laugh at beer-swilling trigger-happy Neighborhood Watchers…

MPAA Rating: R for some strong sexual content including references, pervasive language and violent images

Cast: Ben Stiller, Vince Vaughn, Jonah Hill, Rosemaire DeWitt, Billy Crudup, Will Forte, Richard Ayoade

Credits: Directed by Akiva Schaffer, written by Seth Rogen, Jared Stern and Evan Goldberg. A Fox release.

Running time: 1:42