In Who Was That Lady (1960), Janet Leigh plans to divorce Tony Curtis after catching him kissing a student, so Tony turns to pal Dean Martin (who's a tv writer) to come up with a plausible excuse for his indiscretion and so save his marriage. Big mistake. Dean convinces him to tell her that he's an FBI agent, and he was kissing the student in the line of duty. They get a fake ID and a gun, and Janet falls for it. So much so that Dean decides they can use this excuse for further "approved" dalliances. Tony is a pushover and lets Dean overrule his objections. Much craziness with the real FBI and foreign agents ensues.
It's is a very lightweight, but amusing film. Runs a little too long, needs some of the slow romantic stuff cut out, but the ending where Tony and Dean try to sink the "submarine" is soooooo worth it. That scene is priceless. You can practically skip the rest and just jump to the end. Though then you'd miss James Whitmore and he's awesome. Man, he plays the best straight man in this movie as a real FBI man. His reactions to the situations totally cracked me up. Dean Martin and Tony Curtis make a great pair. Too bad they didn't do more together!
(The DVD also had another Dean Martin movie, How to Save a Marriage and Ruin Your Life which I made the mistake of watching. A confused muddle. Starts as a mistaken identity movie, switches into a battle of the sexes movie, never succeeds at either, sends many mixed messages, and Dean didn't even sing the title song. Hmph. However Eli Wallach was pretty darned funny and had the best moments in the movie, and dude! Stella Stevens looks so much like Barbara Eden it's uncanny. Or Barbara Eden looks like Stella Stevens.)