Unless it's a fantasy or a particularly weird science-fiction film, a movie just won't work without some atmosphere of believability. So when the title characters of "Two Girls and a Guy" can't convince anyone they're involved with each other, there are some serious problems.

Actually, all three leads in this lame sex comedy/drama are so annoying and unlikable that it's hard to believe anyone else would want to date them. That's certainly not enough reason for the movie to go on, though.In fact, the whole thing is so amateurishly staged and paced that it looks and sounds more like an awful student production than anything else. And let's face it, the love triangle thing has already been done to death.

Robert Downey Jr. stars as Blake Allen, the crux of the triangle. This film star wannabe (who sure has a posh spread for being such a second-rate actor!) has been stringing along two girlfriends at the same time, flighty Lou (Natasha Gregson Wagner, daughter of the late Natalie Wood) and the more reserved Carla (Heather Graham, from "Lost in Space").

Both women meet while waiting for Blake to return from a Hollywood trip and quickly discover what they have in common. Breaking into his apartment, the two women plan to confront him.

You can probably guess where this is going. When Blake finally does show up, he pleads his innocence and, that strategy failing, tries to work his charm on the duo.

Writer/director James Toback (1989's "The Big Bang") had to cut one lengthy sex scene to get an R rating, but there's a lot more that should have been pruned, beginning with Wagner's shrill and lousy performance.

Of course, Graham and Downey aren't really that much better (though he does have a couple of funny moments) - they just seem that way because their co-star is so horrible.

To be fair, it doesn't help that they're reading Toback's dialogue. And his ending is such a huge copout that it seems to defeat the whole purpose of the movie, which seems to be that guys can be heels. Wow, what a revelation!

"Two Girls and a Guy" is rated R for profanity, two simulated sex scenes, vulgar sex talk and gags, violent slapping and brief gore.