I was sexually harassed at work yesterday

You did what you had to do. Don't get me wrong, I'm not defending them. They were obviously being dense. If something like that happens again with someone else, I'd say "Hey! Knock it off or I'll have to take this to HR." That will put a stop to it.

Are we talking about a co-worker?

I am a man, probably 15 years younger than you, and not American. No idea how informal office rules are, but just explicitly spelling out that he's crossed the line where it's flattering and just comes off as a desperate creep reciting pick-up lines should probably work? Stay distanced (!), i.e. don't come across as overtly invested, but maintain the impression that you are in control of the situation, and bluntly (but not overtly emotionally so) tell him that he's out of line and acting in a manner that paints him in a really pitiful light. Don't go to great length to explain yourself, either. "Now excuse me, please, I have to go back to my work. I'm sure you'll respect that and don't want me to file a formal complaint", or something along those lines. You don't need to give a reason to NOT want to talk to him!

I mean, from MY EXPERIENCE, nothing crushes guys like telling them that their actions make them look WEAK. If you tell a guy that he makes you uncomfortable, well, that's confirmation that he intimidates you - he comes across as an intimidating guy! For somebody who's desperate enough to go for harassment, that is a form of validation. Tell him that he comes off as a douche and as a loser, and keep it short. Don't give off the impression that you're investing more energy into this than them - give the impression that they are trying with all their might, and failing. Not that one off-the-mark comment from them will keep you busy all night. Even if that's the case, that implies that very form of power they crave. (If you're a guy and put down other guys like this, be ready for some mighty rage.)

ETA: Also, two things:
1. Sorry to hear that you had contact with such a sleazoid and got into such a shitty situation.
2. DO NOT BLAME YOURSELF. Be your own ****ing advocate and ensure that you're not selling yourself and your rights short out of "courtesy" just so he can be an idiot without consequences.