Some bad ideas in the world of popular music suffer a short shelf life.

Hair metal. Gangster rap. Synth pop.

Keyboard neckties. Platform shoes. Japanese headbands.

Eddie Murphy’s singing career.

Other bad ideas linger longer than a flattened skunk. In fact, some are so prevalent that few people ever stop to question why they’re still around.

Here are a few tools, concepts and artistic choices that continue to be implemented by entertainers … and continue to hound listeners, whether they realize it or not.

RECORD SCRATCHING

Take a step back from the pervasive use of a turntable to scratch records, and you’ll realize it is modern music’s silliest and most irrelevant instrument.

Why not bring a vacuum cleaner onstage and turn it on and off? Or how about employing the tones of bread popping out of a toaster?

How this practice, which doesn’t even make a particularly cool sound, has earned any street credibility over the years is a mystery. The most untalented bass player in a high school punk band usually has more musical validity than a hipster making noises with his Technics.

Respectable examples: Run DMC, Beastie Boys, Beck

Worst offenders: They’re all pretty irritating, but the sound of Limp Bizkit incorporating scratches into hard rock anthems is especially icky.

CHOREOGRAPHED ROUTINES

All the artists who feature more dancers onstage than musicians need to rethink their profession.

Live music is about spontaneity. It’s about being able to interact with the fellow musicians onstage and with the audience in new and vibrant ways during each show.

There is a word for synchronizing a routine to four-minute pop songs: cheerleading.

Respectable examples: James Brown

Worst offenders: Madonna, Jennifer Lopez, boy bands

HARMONICA NECK HOLDERS

No, that’s not a correctional dental apparatus from the 1950s. It’s a harmonica neck holder.

The device is usually employed by singular folk musicians as a means to break up the monotony of protest songs being warbled over three chords.

But anything that encourages people to play harmonica who don’t know how to play the instrument is a bad idea. (Remember Alanis Morissette squawking her way through “Hand in My Pocket?”)

The neck holder is a hands-free invention that ranks right up there with the beer guzzler hat.

Respectable examples: Neil Young

Worst offenders: Many acoustic folk musicians, including Bob Dylan

FEAT.

A quick look at the Billboard singles chart reveals a shared trait: Half of the top-10 tunes employ the term “feat.” (for featuring) when crediting the performers.

These include Kanye West (feat. Jamie Foxx), Missy Elliott (feat. Ciara and Fat Man Scoop), The Pussycat Dolls (feat. Busta Rhymes), Bow Wow (feat. Ciara) and 50 Cent (feat. Mobb Deep).

Time was that an artist could put out a single without having to resort to name-dropping in order to get on the radio. Now these pairings are virtually a necessity. They also reek of record label intrusion, in which the company tries piggybacking an emerging artist on the success of a more established one. Half the time the musicians don’t even know each other until they’re introduced in the studio.

Respectable examples: Dido joining Eminem on “Stan”

Worst offenders: Kanye West resorting to raiding Hollywood for musical partners

LIP-SYNCHING

You would think past fiascos such as Ashlee Simpson and Milli Vanilli might have served as a lesson to others in the industry. (Anyone who thinks Simpson’s career hasn’t been affected should check out those minuscule box-office numbers for her latest star vehicle, “Undiscovered.”) But as long as the public is willing to put up with pop stars who can’t sing, they’ll have to endure paying $45 for concert tickets and watching the star play make believe to prerecorded tracks.

Just ask Hilary Duff how the formula works.

Respectable examples: Umm, maybe if you’re shooting a video

Worst offenders: Simpson’s “Saturday Night Live” meltdown

WAH-WAH PEDAL

Technically, this device “sweeps the peak response of a filter up and down in frequency.”

In layman’s terms, it’s the thing that makes the guitar go “wah-wah.”

Believe it or not, the wah-wah pedal was first popularized in country music before the psychedelic rock musicians of the late 1960s laid claim to its caustic sound. (The soundtracks to stag movies then followed suit.)

But even with all the digital doodads available to modern players, the cheapo effect refuses to die. It also can be used as a barometer for when the “lead” guitarist in a band can’t solo. His lack of skill is directly proportionate to how fast he steps on the pedal to disguise the fact.

Respectable examples: Cream’s “White Room” or Jimi Hendrix’s “Voodoo Chile (Slight Return)”

Worst offenders: Just turn on 98.9 FM

MELISMA

You might as well rename it “American Idol Syndrome.” Melisma involves straying from the melody in order to force-feed several notes into one syllable of text.

And it has become the bane of the pop R&B culture. When it’s done with skill, it seems like showboating. When rendered poorly, it can derail a song.

Frustrated sports fans know it can also stretch an interpretation of “The Star-Spangled Banner” by several minutes when you are waiting for the first pitch.

Respectable examples: Stevie Wonder, Al Jarreau

Worst offenders: Christina Aguilera and her ilk

Very bad things runners-up: fog machines, drum solos, samplers, fade-outs, hip-hop skits between recorded songs, rhyming “night” with “all right,” tribute albums.