So, you ask, how should I, as a single person, spend this ridiculous day?
Enjoy the fact that you're unencumbered and have no one to impress. Don't shave. Leave the expensive perfume in the medicine cabinet. Wear sweats. Order a double-onion pizza, and follow it up with an entire bag of those delicious pink and white M&M's. Fart as loud as you can. (Just, you know, be careful... you don't want to gamble and lose.) Marathon your favorite bad show. Hog the remote. Cuddle your pets. Go out and see a movie by yourself. Indulge in some self-loving. Wallow in it.
In case you're wondering what I mean by that, it's exactly what you think. Knock one out. Have a wank. Masturbate. Watch your favorite porn, fire up your favorite battery-powered toy, or just light some candles and run a bath. However you enjoy it most, do it. I bet you'll have a better orgasm than most of the couples out there. 'Cause you have nothing to prove to anyone.
Whatever you do, don't be hard on yourself. Don't feel bad because you're single.
If I sound cynical, it's because I am. Valentine's Day is unfair. It's an insidious thing, and you shouldn't let it get you down just because you don't have a significant other. You're not worth any less because you're not half of a pair. You're a whole, beautiful person all on your own. The gross truth about Valentine's Day is that it is a celebration in exclusion, an arbitrary day on the calendar that gives the false impression that you're more important if you're coupled off. After all, you don't see any days devoted to celebrating single people.
Just as bad, it puts pointless pressure on couples to prove their worth as a pair by having them exchange flowers and candy hearts. Even on those rare occasions when I have been part of a couple on Valentine's Day, it felt totally false and forced. The little gestures people feel they have to make on this one specific day would have so much more meaning if they were spontaneous, driven by love rather than obligation.
Celebrate the day however you like. I'm going to spend it being proud that I can exist as a singular entity, that I don't need another person to complete me. Mostly, I'm not going to do anything at all.