The title of Piranha 3DD, the sequel to 2010's Piranha -- itself a remake of a little known 1978 B movie of the same name -- should tell you all you need to know about it. It's crass and campy -- not the type of thing to take Grandma to see. (Really, please don't take your Grandmother to see it, assuming you can find it at an actual theater.)
Still, Piranha 3DD is so brazen in its utter ridiculousness -- its balls so brass and big, to paraphrase Stephen Colbert -- that I feel like I should tell you a few more things about it before you decide to go and see it (or rent it from Amazon, which is probably the easiest way to get your hands on it at this point).
First, there are three noteworthy cameos that are sure to get your attention mostly in a how-the-mighty-have-fallen sort of way. Gary Busey fills the role Richard Dreyfuss did in Piranha -- the noticeable face first savaged by the deadly piranhas before they are unleashed on a larger population. Christopher Lloyd reprises his role from the original as Mr. Goodman, the shut-in scientist who knows everything there is to know about the prehistoric, murderous piranhas that tormented Spring Breakers at Lake Victoria in Piranha and the patrons at nearby "Big Wet" water park in Piranha 3DD. Finally, David Hasselhoff plays a startlingly realistic version of himself, the Baywatch star reduced to making personal appearances at backwater venues to earn a living (go ahead and figure out whether I'm talking about him or his character in the movie).
Second, there is the staggering, naked (pun intended) exploitation on display throughout. There are numerous slow-motion shots with the camera focused squarely on cleavage. There are several memorable decapitations, including one of a young boy that concludes the film.
Third, there is Ving Rhames, who, like Lloyd, is one of the few holdovers from the first film. Rhames' character, Deputy Fallon, lost his legs in the original. Naturally, he returns in the sequel with the ability to turn one of his prosthetic legs into a machine gun -- an ability that, of course, gets put on display within minutes of his appearance on-screen. It would have been more awesome if I hadn't seen it already from Rose McGowan in Grindhouse: Planet Terror, but I'm not going to complain about Ving Rhames with an automatic weapon as an appendage. It's just a rule I have.
Fourth, there is a ... well, a piranha pregnancy. Katrina Bowden's character Shelby somehow ends up with a piranha spawn in her womb that then bites the member of her lover, who promptly responds by going all John Bobbitt on himself. (If you can't figure out what I'm talking about you're either too old to see this movie or not old enough.)
Beyond that, it's impossible to really recap Piranha 3DD. If it were a house it would be held together by toothpicks and duct tape. Even compared to its predecessor, which I would argue is pretty great as far as campy, self-aware horror goes, there's little in the way of plot and nothing in the way of a central theme or message.
It's entertaining, at times wildly so, because it is so absurdly bold and made without even remote regard for taste. But it's entertaining only because its very existence is surreal, not because it has genuinely funny moments or a halfway decent plot like the original Piranha.
Like I said at the beginning, the title really tells you all you need to know.