(Photos by Bauer Griffin, Flynet Pictures, Getty Image)We've all seen it. The embarrassing moment in a pop star's career where the music just doesn't quite match up to what their mouths are doing. From teen idols to rappers with a reputation for being tough guys, the horrors of lip-syncing befall even the most famous names in music, proving that topping the charts or selling out arenas is more a factor of image and production value than a reflection of actual musical talent.These guys know what I'm talking about. On the one hand, lip-syncing is understandable–you have to be in some seriously good shape to do choreographed dance numbers and simultaneously sing like you do on your albums. Although when that's the case, it's better to just be upfront with your stage show rather than act like you're giving the audience the genuine article. But so many times these stars get caught faking it when they just as easily could have actually been singing, unless of course (gasp) they can't actually sing.It's time we ran through some of the best moments in lip-syncing history.Milli VanilliSure, lip-syncing existed long before '80s duo Milli Vanilli came around, but they are the quintessential example of career-ending lip-syncing controversies because it exposed them not only as live show fakers, but also as complete recording frauds. The infamous Rob and Fab, who fronted Milli Vanilli, never actually sang a note on any song, live or otherwise. It was some other dudes who weren't so, shall we say, aesthetically pleasing. The Milli Vanilli dream came crashing down that one infamous night when their vocal tape jammed.I know, what a mess. Lindsay LohanRemember back in 2004 when Lindsay Lohan was still pulling off the well-adjusted routine and was kickstarting her venture into a music career? You mean you don't remember her classic song "Rumors"? That might be because 1) it was an absolutely horrid song, and 2) because LiLo lost quite a bit of credibility when fans realized all her performances were clearly just a recording and she couldn't really sing without some major studio help. As you can see from the clip below, even her youngest admirers seem sadly unimpressed when Lindsay forgets to move her mouth (particularly in the 2:10 to 2:30 stretch).Oh, those poor guys in her backing band. They probably had dreams of following in the footsteps of rock's greats, and here they are stuck trying to add "edge" to a song about a rich and famous girl's need for privacy despite constantly using the press to further her image and career. I can't help but think that with every headbang they think to themselves, "Oh god, I totally sold out."Jude Law, disgusted by Ashlee's oops. Ashlee SimpsonThe last video above is conveniently titled "Lindsay Lohan pulls an Ashlee Simpson" because earlier that same year, Jessica's little sister found herself in one of the biggest lip-sync fails in pop music history, and she did so on national TV no less. Simpson was all set to perform her second song of the night for Saturday Night Live when the backing track for the song she already played came on instead. Although her band rolled with the control room's mistake (because they can actually play), Ashlee was too thrown off to fake faking it. Her only resort to cope with the embarrassment was to dance a ridiculously awkward jig.Be cool, 50... be cool. 50 CentEven the toughest guys in hip-hop can be made to look impotent and silly when their pre-recorded live performance backfires on them. Just ask 50 Cent, who took multiple gunshots to the chest, but still needed a backing track when he performed live at the BET awards in 2007. The rapper's cover was blown when he repeatedly missed his cues and fell victim to a technical mishap that left the music playing in a loop without the expected recorded vocals to go along with it. The whole thing was a mess, but 50 just kept struttin'... no shame in his game.No flute for you. Katy Perry

Katy Perry is the most recent egregious violator of the lip-sync slip-up, although Perry's oops moment didn't even involve her singing, and it might actually be a calculated part of her live show. Perry got caught when she forgot to "play" what she called a flute (even though it's real a bedazzled recorder) along with the backing track. Although footage of the mistake makes Perry look pretty embarrassed as she admits, "Okay, I lied; I can't play the flute," there's conflicting reports as to whether or not the gaffe was on purpose. Perry supporters contend that it's a planned joke that is part of the show. Either way, it's still funny and proof that little damage is done when you actually own up to what you can't do.Lady GagaAs we said earlier, performers who are more about show than voice or who have to dance and get all theatrical at their concerts somewhat have a pass when it comes to using a backing track for their vocals, but Lady Gaga lost her shot at such a pass when she went on this self-righteous tirade:Okay, we get it. Lady Gaga has a great voice, and she's proud that her fans get genuine singing when they come to her shows. But it seems pretty clear to me from the footage below that Gaga isn't living up to her promise of being 100 percent real 100 percent of the time. I mean, in one video, the vocals stay the same no matter where the mic goes (suspicious), and in the other, she biffs it hard and doesn't miss a note (impossible).Mariah CareySimilar to Gaga, we all know that Mariah Carey can sing; she's proven herself enough, and also like Gaga, Carey has gone on record saying that she would never be part of the lip-syncing trend because her music is "all about the singing." Which is why it's confusing to see that Carey very obviously lip-syncs her way through her latest performances and self-indulgent vocal runs. Maybe she's lost it. Carey doesn't even have the excuse that she's dancing during her shows since she can hardly walk down three steps without assistance.What'd ya expect? Britney SpearsThis list wouldn't be complete without one of the queens of lip-syncing: Miss Britney Spears. Is anyone still being fooled by Spears' blatant use of backing track in everything from her stadium tours to her talk show performances? The thing with Spears is that she doesn't even dance anymore, at least not like she used to. She just kind of wiggles in one place, which means the aerobic workout of a stage show is no longer a legit excuse for phoning in the vocals. So now she can't sing; she can't dance, and she no longer gives interviews. How she remains relevant is baffling.