Unfortunately, only certain people I know are even aware it exists. It is a breakout internet phrase, but you can sit in the pub and say something like "Well, the Indian Premier League has really jumped the shark, eh? Flaming helmets for badges, what's that about?" and be met with nothing but blank stares. Admittedly my local pub is an Irish pub in Austria so discussions about cricket clothing tend to be met with blank stares anyway, but we do have a cricket club here in Steyr so I can be fairly confident that it's the shark jumping that's not being understood.
SO you have to give a little potted history "Happy Days", "Fonzie jumps a shark", "series goes downhill", "some college kids turn personal slang into snark-filled website". You know... Sort of like how, no matter how mainstream it gets, someone will always feel the need to explain what "Schadenfreude" is, "jumping the shark" comes with its own ritual explanation. This, of course, mitigates against its usefulness as a cute phrase covering a not-too-complicated phenomenon.
That said, "jumping the shark" does somehow suggest what it means even if you don't have an American college student's encyclopaedic knowledge of seventies US-sitcoms.
There are already an number of variants, and now, because you're nobody on the Internet unless you've coined at least one phrase (I have a small claim on "mid-life goatee", not that anyone has noticed), there is a challenger for jumping the shark. You may have heard it already, or, perhaps, you just don't care about what a bunch of media geeks are patting themselves on the back for these days. Anyway, it's this:
Nuking the fridge
This probably gets a little more recognition because more people are familiar with Indiana Jones movies and the latest one is a comparative disappointment that does have a scene where Indy survives a nuclear blast by hiding in a lead-lined fridge.
The New York Times already has an opinion on this.
Hence, "to nuke the fridge" means to introduce a wildly implausible element to a once-respected franchise, or more generally, to signal the abandonment of past standards of quality.
There's even a bit of snark over the qualities of the two phrases:
"'Jump the shark' is for people over the age of 60, who remember the show," he [the owner of "nuke the fridge" website] said, adding that "nuke the fridge" was a "new, fresh take."
Again this doesn't really survive the pub test (I know, how delightfully parochial of me): "Hey have you heard 'nuke the fridge' is the new 'jump the shark'?" Cue more blank stares and about half an hour of rambling explanation.
It doesn't quite work though, does it? I mean Indy found the Holy Grail, dug up the Lost Ark and got through a whole movie without punching Short Round in the face; a nuked fridge is not so much introducing a wildly implausible element as adding another one to the list. It's not even the point in the movie that puts the franchise at risk (and it's not a bad movie, it just wasn't good enough), well, any more than, say, the prairie dog reaction shots, the clumsy lingering over Connery and Elliot images, Shia LeBeouf or the fact that you can imagine Spielberg and Lucas mirthfully stroking their beards over how clever it is that in this movie Indy's not searching for something, he's taking it back. Though I admit none of those particularly lends itself to cute phrasing, the closest I got was "pointless capoeira in the graveyard".
I don't know, it seems to be one of those phrases that is discussed rather than used.