The first thing in Todd Phillips's comedy's favour is the fact that Judd Apatow and his particular brand of puerile antics (The Hangover's still puerile, though) are not involved at all.
Secondly, it has the funniest use of a tiger (in a hotel bathroom) ever.
Stu (Ed Helms), an uptight dentist who's verbally and physically bullied by his horrid girlfriend, Phil (Bradley Cooper), a cocky, sleazy teacher, decent groom-to-be Doug (Justin Bartha) and Alan (Zach Galifianakis), the stag's insane brother-in-law ("a one man wolf pack" who doesn't care "if we kill someone"), drive to Las Vegas for Doug's bachelor party. They get wasted. So wasted that they've lost the stag the next morning, and have zero memory of the night before. However, they're left with "clues" – a tiger (Mike Tyson's tiger, in fact) in the loo, a baby in the cupboard, a roaming chicken, a lost tooth and a missing mattress – as to what might have occurred in their obliterated penthouse suite at Caesars Palace.
This energetic, anarchic and droll – it's full of great one-liners, especially from Alan ("It's not illegal, it's frowned upon, like... masturbating on an airplane") – Vegas farce benefits from a convincing chemistry between the four men. Their sparring, sniping and ribbing feels genuine, and Jon Lucas and Scott Moore's perky script doesn't flag; unlike all of Apatow's comic adventures.