Revenge is a dish best served cold. Or, in Seven Psychopaths — writer/director Martin McDonagh’s disappointingly half-baked follow-up to In Bruges — slightly reheated.

Billy (Sam Rockwell) and Hans (Christopher Walken) are two miniscule-time grifters whose dognapping scheme goes south after they nab Bonnie, a Shih Tzu belonging to Charlie Costello (Woody Harrelson), a hotheaded, vindictive gangster.

This rogues’ gallery of goons turns in vividly unhinged performances — complementing violent vignettes with eruptive laughs and exploding heads. Walken blends his vintage-wackadoo verbal hotheadedness with a stoicism and sweetness, and add “hallucinogens” to his Canon of Comically Mispronounced Words. Harrelson hams it up as a cold-blooded, contemptuous cur whose world is nevertheless centered by his Shih Tzu.

Rockwell again dances a line between hapless dope and demented genius, almost like a Walken 2.0 as he utters an indelibly hard-boiled bon mot: “I didn’t mean to break his nose. It was just in the middle of where I was punching.” Plus, as a bunny-stroking killer of killers, Tom Waits has a demented monologue of his own.

Were the movie really about them, it would be a passably entertaining post-Tarantino crime comedy with a potent surprise or two, just 15 years after post-Tarantino crime comedies with a potent surprise or two became passé.

If only the movie were about them. Instead, it’s primarily about an alcoholic screenwriter who’s Billy’s best friend. And not any screenwriter, but one named Martin (Colin Farrell, eyebrows working overtime to elevate the straight-man role he’s given) struggling with a screenplay called Seven Psychopaths.

Is this well-tumbled-down rabbit hole starting to sound familiar?

“I don’t want it to be another film about guys with guns,” Martin pontificates. “I want it to be about love and peace … but there still have to be psychopaths.” This is the cake McDonagh also wants to have and eat. And he pulled it off in Bruges, which became a palpable parable about purgatory.

But here, the contrivances of Martin’s creative struggles, real or fictional, stack up like a jammed Tetris board. And by almost tripling the amount of characters he worked with in Bruges, McDonagh can’t keep up with the pace.

Just because Farrell’s Martin is criticized for writing weak female characters doesn’t exactly let McDonagh off the hook for wasting both Abbie Cornish and Olga Kurylenko. And you can’t say the film doesn’t self-referentially warn you about the majority of its final hour — a talky detour into Joshua Tree National Park where Billy and Hans each take a crack at fleshing out the themes of Marty’s script. It feels like the third act of Adaptation. stretched to a tiresome length.

Ultimately, the experience of watching Seven Psychopaths is akin to watching a dog like Bonnie chase its tail: It’s only funny until you realize that the running in circles isn’t ever really going to stop.