Have you told him you're not interested? I understand that you think your behavior should communicate this, but different people communicate differently and it's possible that he doesn't realize you don't appreciate his behavior.

If you haven't, consider sending him an email (or approaching him the next time you can if email isn't an available option) explaining "I don't like the way that you are treating me. I am not interested in a romantic/sexual (pick one) relationship with you and I do not flirt. Please stop trying to flirt with me, do not under any circumstances touch me without my consent, and interact with me in a strictly professional manner from now on. Do you understand what I am asking of you?"

Assuming he responds in the affirmative continue with something like: "Great. I hope a I can look forward to a positive professional relationship with you from now on."

I've found this sort of formal request that someone change their behavior really valuable both in terms of getting people to understand that a cultural/religious/communicatory/whatever difference that they may have made light of is a big deal and will be taken seriously, and so that if the problem persists I can inform HR "On such and such a date I told so and so, quote, (read quote. Have a printed copy of the email if an email was possible). He indicated to me that he understood my request. On new date he did new bad thing. It seems to me that this is (prohibited behavior category). What are we going to do about this?"

I've also found that informing HR as soon as possible makes asking them to take action later a lot easier. If they know that you've tried being reasonable and it's failed they are more likely to think of you as the reasonable party and more likely to take your complaints seriously. If you can go the email route, I'd definitely CC HR and apprise them of the situation.

If you've already done this or something like this, it's time to report this as sexual harassment. If you've already done that and somehow nothing is happening, it's time to talk to an attorney.

Talk to the Police

With your edit, this no longer sounds like 'persistent annoying' behavior but rather extremely threatening, dangerous behavior. If I was you, I would be afraid for my safety.

In the state I live, getting permission to carry a weapon on company property is basically impossible, but if that's something that is a real option for you I'd definitely consider it.

I would call the police (non-emergency), and ask for a restraining order. I would then call a lawyer specializing in workplace harassment or women's rights issues and ask to talk with them about this ASAP because I'm worried for my safety. If they couldn't give me preliminary advice quickly, I'd find someone else.

My default plan would be to contact my CEO, explain what happened, especially the 'spanking' episode and the 'you want me, you just don't know it yet' creepy talk. I would then refuse to go into work until the sexual harrassment situation is dealt with. I would explain that I am afraid for my safety and until the company can provide a workplace free from sexual harassment I will not be coming in to work.

If I had any friends at work, I would tell them (via phone or email, obviously, since you aren't going in to work) what was happening and ask them, if appropriate, if they would be willing to cover parts of what I was working on until the company decides what it's going to do about the sexual harassment. Something like:

"Hi, Tom, So John (the creepy stalker guy) has gotten pretty serious with his threats and I don't really feel safe coming to work right now. I'm hoping the Boss will take care of it soon, but it doesn't really feel like he's listening to me. In any case, I'm going to be out of the office for a few days at least, do you think you could handle (one of the things you were going to do that John is also qualified to do) for me? It's alright if you can't, I'm just supposed to have it done so (larger project) can go online by (date).

Also (appropriate additional communications based on your relationship and trust and desire for support from this person and whatnot)

(your signature email ending thing or lack thereof)"

Once I heard back from people, I would email my boss and be like "Hey, so I got Tom and Dennis to cover (thing A) and Paul said he'd be willing to do (thing B) if he has time. I couldn't find anyone to cover (thing C), though. Hope I can come back to work soon."

If you want to take matters into your own hands, what's being done is almost certainly a violation of several criminal laws in California, may be a violation of several others, and may lead to additional criminal violations. Specifically, Stalking, Violation of a Restraining Order, Criminal Threats, and Sexual Assault.

There are also several civil violations, such as civil harassment, that are relevant here. Criminal problems you can get solved by talking to the police by yourself. Civil problems are more likely to require a lawyer (which you should be getting anyways at this point).

I would also make sure to lock my doors and windows, and to travel with friends when going out.

To reiterate, this sounds like a serious and immediate threat to your personal safety and you should react appropriately.