“The Watch’s” woes can’t be blamed on lousy timing.

The high concept comedy endured a hasty name change from “Neighborhood Watch” to simply “The Watch” when the Trayvon Martin case blew up in the media, and suddenly citizens defending their turf became too sensitive for a big screen comedy.

What hurts “The Watch” far more than that marketing meltdown is its own lack of purpose. The comedy alternately sends up suburbia, mocks alien invasion movies and taunts modern bromances before finding its ill-fitting destiny – to out-“Hangover” “The Hangover.”

Yes, it’s that crude, but at least “The Hangover” scenario warranted those hard-R antics.

Holding it all together is its cast, a group of comedy all-stars who will all move on from “The Watch” and likely never look back.

Ben Stiller plays Evan, a by-the-book Costco manager (“The Watch” doubles as a bulk food infomercial) who is shocked to learn his colleague has been murdered. Evan vows to find the killer, and he instigates a neighborhood watch program to nab the cretin behind the crime.

His sales pitch nets a trio of neighbors (Vince Vaughn, Jonah Hill and “The IT Crowd’s” Richard Ayoade) who would rather chug cheap beer than waste their time on a stakeout.

Together, the watchers take down a nefarious ring of egg throwers before stumbling onto something far more sinister, a bona fide alien invasion. Any alien race that can’t outsmart these guys doesn’t deserve to pillage our planet anyway.

“The Watch” traffics in crude gags and puns, the kind Judd Apatow might consider before punching the “delete” button on his keyboard. Bodily fluid gags abound, and the dialogue plays out like a Mad Libs game filled in by pre-teens in the grip of their first hormone wave. 

Tonal discrepancies are a more serious matter, from a marital crisis between Evan and his wife (“Your Sister’s Sister’s” Rosemarie DeWitt) to the gang posing for pictures with a deceased alien. It’s the latest example of kitchen sink comedy, a sign that so many screenwriters pitched in that no one vision emerges.

For the record, overrated scribes Seth Rogen and Evan Goldberg polished the original script by Jared Stern, although “Iron Man 2” screenwriter Justin Theroux apparently took a whack at it as well. 

“The Watch” works best when the leads are riffing on their natural strenghts. For Hill, that means dense but softly uttered dialogue that’s both whipsmart and more than a bit daffy. Stiller is still milking his mensch shtick, and when played against Vaughn’s boastful banter it’s a mighty weapon.

Some of the best bits feel improvised, like when Stiller and Hill play Bad Cop, Worse Cop on a shaken egg thrower.

“The Watch” moves swiftly, features a few genuine moments of suspense and showcases a cast with an enormous war chest of audience good will. It’s still a mess, the kind of slapdash project stars of this magnitude should have passed along to unknown actors eager to make their screen debuts at any cost to their self esteem.

Follow Christian Toto on Twitter @TotoMovies