Valentine's is overrated. The candies and chocolates are nice and all, but you can get them year 'round. Not so much in the heart-shapes, but aye, they're always around. It's the over focusing on the romantic shite that's the problem. If you do the love thing, love year 'round. Sure, nothing wrong with doing a little more on certain days.
The real problem is, if you aren't attached in some way, finding a shag on Valentine's is hit or miss. You either get the desperate flinging themselves in your path. All well and good if they're fit, but you might end up with a clingy one who thinks you're suddenly a couple just because you shagged once. Shagging isn't dating; a shag is a shag is a shag. 'S all it is, 's all it's ever likely to be I was shagging them. It's bloody hard to try to let someone down easy when they're wanting to be all cuddly and post-coital lovey-dovey. And they get all upset when you tell them it didn't mean anything at all to you and suddenly you get a lecture about love and life and happy rainbow bunnies and you're thinking, "My God. I'm really glad I didn't take him back to mine", because then you'd have to manage to make him get dressed and kick him out. So much easier being able to get dressed and get the bloody hell out while he's still going on and on and on.
So I suppose all I've really got to say is, if you aren't in a relationship of some sort, don't shag random people you don't know on Valentine's. Any other day of the year you can have at it, but not Valentine's. It's messy and not in the fun way.