Men have it easy when it comes to date outfits, insofar as male sartorial standards have fallen so low that just showing up in something other than shorts will be considered progress, and that just going for something modest, classic, and well-fitting will be considered dashing.
But why stop there? Rely on texture and contrast. A good date outfit says two things. The first is, "I care enough about you to think about what I'm wearing." The second is, "You're the pretty one in this expedition." You want to avoid flamboyance, but you also want to show that you care.
So find yourself a pair of trim wool charcoal pants. Wear a good white shirt with a spread collar. Pair the white shirt with a slim solid burgundy tie.
Here's the part that will give you pause: wear a black or chocolate blazer. In velvet. If velvet feels like too much, a good alternative is an unstructured blazer in black coated selvedge. But velvet is appropriate as long as the outfit as a whole doesn't overdo color or patterns. And see that top pocket on the jacket? It's for a pocket square - a pink or rose one, in this case.
Executed right, you'll find yourself wearing a limited color palette (black/charcoal, rose/burgundy, white) but a decadent range of textures: cotton, wool, silk and velvet. Your date will, at various points, lean in to inspect and touch each of these fabrics, which is the whole point of wearing them. We wear clothes to eventually - if all goes well - take them off.
If there was ever a day to go all out for a date, it's this one. After all, you've had years of insistence from Hallmark and Russell Stover that this is the grandest excuse to forget it's the bleak middle of February and give yourself over to love, sweet love. If you've got a date that doesn't involve a pint of Ben and Jerry's and your BFF Carrie Bradshaw, consider yourself Hallmarked and attack V-Day with all the glamour you've got.
How? Look to great sirens of the past for inspiration. If he hasn't yet proposed, remind him that diamonds are a girl's best friend and go full-on Marilyn Monroe: strapless satin gown, elbow-length gloves, fake fur stole, and voice in a husky purr (not all that hard to fake in cold season). Curl your hair up in gorgeous waves and accessorize with only costume jewelry, the better to remind him that you require the real thing - and promptly. If your husky purr is more of a rebel yell, stand out in a crowd of red and pink cupcakes and steal the style of Morticia Addams, matron saint of gothic glam. A floor-length black gown is guaranteed drama, whether your preferred fabric is flapperesque lace or pettable black velvet. Pair it with red lipstick and a cozy shawl (or a cape!) and you'll have your own gentleman calling you cara mia.
Should gowns be inappropriate for your planned evening, try adding a little soul to this corporate holiday and emulate Billie Holiday with some fabulous '40s flash. Flowers in the hair are, of course, key to this look, so splurge at the florist's for big white gardenias you can pin above your ear. Skip the perfume and let the gardenia scent draw him in.
A simple '40s-style dress completes the look; think nipped-in waist and shorter heels to go along with it.