Marlo Thomas triumphs, 'Sex Tape' flops and Ann-Margret still sizzles.

'S ex is an emotion in motion," said Mae West. And speaking of sex, movies centering on that theme can be fun or frolicsome or tiresome or unpalatable. But like vampires, super-intelligent apes or (more recently) zombies, the sex comedy genre never grows old. Although now they are often referred to as "rom-coms" (romantic comedies.)

However, even the best-laid (pun intended) plans of studio and stars can misalign. This weekend's disastrous box office on the Jason Segel/Cameron Diaz "Sex Tape" movie being a prime example. It's not as flat-out awful as the box office and some of the more dismal reviews suggest, it just doesn't know to what it aspires. Whether to be utterly gross, or amusingly accessible slapstick. It ends up being nothing much at all. Mr. Segel and Miss Diaz are appealing, but can't save a shaky, basically unfunny premise. Not even with the presence of Rob Lowe, inescapably and deliberately evoking his own sex tape scandal way back when such things were shocking.

I keep telling you that our longtime friend Marlo Thomas is a largely unsung wonderful actress!

Besides creating just about the first independent female on television in "That Girl" long ago, she was the best thing seen on Broadway in 2011, enacting a selfish know-it-all in Elaine May's little one-act titled "George is Dead." (Let's not bother here to go into all her good works...