No, not the Mr. and Mrs. Smith starring Brad Pitt and Angelina Jolie. This is the comedy starring Robert Montgomery and Carole Lombard, directed by Alfred Hitchcock. Yes, Alfred Hitchcock.
Mr. and Mrs. Smith discover that they aren't really married. I think I saw an episode of The Dick Van Dyke Show that had the same idea, but it was handled very differently. Mr. and Mrs. Smith feud all the time, and it just happens that the day before they find out about the marriage, Ann (the Mrs.) asks David (the Mr.) if he would marry her again if given the chance. He says no. This was, as you might have guessed already, the wrong answer.
You have to know going in that everything that happens after that depends on one person acting really illogically, and that person is Lombard. It's kind of tough to like her and put up with it, but she almost pulls it off, being Lombard. Robert Montgomery is very funny and gets a lot of the laughs, such as they are. Of course you know all along how it will end.
I like the "Not suitable for general exhibition" warning label. The double entendres and mild sex jokes wouldn't raise an eyebrow on a children's show today.
I was amused by the movie, but I didn't laugh out loud. Montgomery has a good scene with a cat in a restaurant that almost did the trick, though.