Anyone have info/advice in regards to business-related harassment?

First and foremost, ask yourself how committed you are to remaining at this job. Is the pay or compensation there worth all of this unpleasantness?

Second, there are laws that govern workplace environment, but they vary from place to place, by case, and by type of employment. All such laws are public record, but ultimately, an attorney would be the best resource here. For the most part, people have the right to say whatever they want, unless it becomes directly threatening to you or others. But no one has the right to lay hands on you. 

Can we assume that you have some discretion to not serve unruly customers, asking them to leave, or barring them entirely? If not, who does? Absent any of these options, it may be wise to seek work elsewhere. This post was edited by Don Barzini at May 18, 2019 9:19 AM MDT

Don't get drawn in by what they say.  Which they do to get a rise out of you so they can feel more powerful.  Be formally polite and do not respond at all.  Go about your business and focus on your duties.  When you complain so often to the owner all she gets out of it is that you are unable to handle it.  Best to not complain at all about such trivialities.  After all the job does not exist for the purpose of your comfort. 

Oh this is so easy.  Accidentally spill drinks on them.  You and your friend.  

This is a lose lose situation.  If you cannot learn to ignore them, harass them back.  Let's see who your boss needs more, them or you.  Get another job.

Assuming you're in the US, yes, the employer is legally responsible. 

An employer may also be responsible for the acts of non-employees, with respect to sexual harassment of employees in the workplace, where the employer (or its agents or supervisory employees) knows or should have known of the conduct and fails to take immediate and appropriate corrective action. In reviewing these cases the Commission will consider the extent of the employer's control and any other legal responsibility which the employer may have with respect to the conduct of such non-employees. https://www.law.cornell.edu/cfr/text/29/1604.11 

The same law on defining sexual harassment: 
Harassment on the basis of sex is a violation of section 703 of title VII. 1 Unwelcome sexual advances, requests for sexual favors, and other verbal or physical conduct of a sexual nature constitute sexual harassment when (1) submission to such conduct is made either explicitly or implicitly a term or condition of an individual's employment, (2) submission to or rejection of such conduct by an individual is used as the basis for employment decisions affecting such individual, or (3) such conduct has the purpose or effect of unreasonably interfering with an individual's work performance or creating an intimidating, hostile, or offensive working environment.

Ergo, if the environment is hostile, intimidating, or offensive to you, or your work performance suffers, it is sexual harassment. You didn't specify how it's impacting you or what was being said, but I would venture to guess this condition fits your situation. 

That said, your employer may not be aware of the laws or simply may not care. It's up to you to decide how to approach it. You have several options. Usually, the best bet is to try to define your own boundaries with the customers in a polite way. That may not be possible if their remarks are really graphic or discriminatory, which is a wholly different thing. But, if they're just drunken come-ons, you can tactfully establish boundaries. Tell them you're seeing someone. Tell them you're not interested. Heck, tell them you're uncomfortable. There are a million ways to address it depending on what they're doing and how they're responding. 

If they aren't responding to your boundary setting or they're really crossing lines and being graphic, the boss should step in. If she's not willing to, even the laws may not matter, but it may be worth gently pointing them out to her. She may well see you as the troublemaker and find a reason to can you though. Yeah, you can sue, but is it worth it? 

You could also find a male employee or male "customer" to have your back. Ideally, someone who is bigger or tougher than the guys being jerks. Have a friend hang out at the bar and just pipe up with a "Hey man, that's not cool," when they say something. 

And, lastly, you could roll with it. I did something similar once. I changed my name at my first job- a restaurant- I gave myself a "stripper name" and half the staff changed their names too. Oddly enough, I didn't care so much about it after that. 

you rnight be able to find that info online