Movies about the mentally ill tend to render them in cute, charming strokes - with only the occasional blast of ugly to remind us, “Oh yeah, this gorgeous, lovelorn soul is still crazy.”

And “Silver Linings Playbook” has a hint of that. You cast Bradley Cooper as a mentally ill man who probably got out of the psychiatric ward a bit too early, and Jennifer Lawrence as a young cop’s widow who isn’t really coping with that fact, and the Hollywood ending is written all over it.

But Cooper gives his most natural, affecting and compelling performance yet as Pat, a divorced ex-school teacher who won’t accept the fact that he’s divorced, or that the school system would never rehire him. People may duck him in amusing ways, but the message is clear. He’s dangerous.

And as Tiffany, Lawrence makes us forget her dewy youth just minutes into her brittle, biting turn as a woman whose unbalanced rage is even more cleverly concealed than Pat’s.

Pat’s mom (Jacki Weaver of “Animal Kingdom”) is the one who has the faith that her son would be better off at home in Philadelphia. His sports-nut dad (Robert De Niro, perfect) isn’t so sure. When Pat pulls a plastic garbage bag over his sweatshirt so that he can jog and lose weight faster, Dad seems to have a point.

“I’m getting really fit for Nikki,” the son explains. That’s the ex-wife Pat expects to win back.

Others aren’t that delusional, which is why the shrill Veronica (Julia Stiles) nags her husband (John Ortiz) to invite Pat, whom she fears and despises, to dinner. She wants the mentally unstable guy to meet her mentally unstable sister, Tiffany. Is Veronica an idiot?

But that jaw-droppingly awkward dinner meeting is where this David O. Russell (“The Fighter”) film takes off. The sparks fly between these two - and not necessarily romantic ones. They have an easy rapport, joking and comparing medications. But Pat’s unshakable belief that he’s winning back his ex, who has a restraining order on him, makes him seem touchier, scarier and further gone than Tiffany. Until testy Tiffany takes a moment to assure us that’s a much tighter race than you’d expect.

Pat has these little mantras he picked up from group therapy and psychological counseling. “Excelsior!” he shouts at random moments when he needs some affirmation.

“If you stay positive, you have a shot at a silver lining.” That’s what he’s looking for in all this.

Tiffany? “I don’t get what I want, OK?” Her volatility is a frightening thing, especially when she feels she’s in a contest. “You think that I’m crazier than you.”

Russell, famous for his own off-camera temper, deftly balances each amusing encounter with tragic revelations and unbalanced moments - threatening to bring matters to an ugly head, or deepen the connection between these two disconnected people. In film and in fiction there’s always a glib cause-and-effect with mental illness - “this” led directly to “that.” We get a little of that here as we’re given the back story and we meet enough relatives to see the trees these two fun but dysfunctional apples fell from.