I've had similar issues -- well, not sexual harassment, but I mean where I've felt the need to leave a place rather suddenly... and then have to explain it later. You are not required to list anything specific on your resume, or in any particular order, or with any particular details. Your resume is your personal thing. But it will look funny if you have this big blank of time in there. I leave things off my resume (and off applications), but not when it creates huge gaps in time to be explained.
Things *do* happen on jobs that can be complicated to explain to prospective employers. If they are reasonable people, they should know everything is not in our control and that stuff happens which is not our fault. I don't put on resumes why I left, but applications usually ask for it, and I write "to be discussed." I'd advise against the "irreconcilable differences" because I think it will look bad, and could imply just about anything. I could pretty well say I had irreconcilable differences at nearly every job I've ever left! (i.e. so what -- it doesn't mean anything.) When they ask why, I'd be honest in a case like this.
If some place really seriously can't understand sexual harassment, then perhaps you don't really want to work for them? As for being slanderous, unfortunately with this sue-happy world we live in, yeah it could be if they can prove some kind of harm. But I don't see how this is harm, especially since you *could* have taken action and didn't even do it. If they ask for details in an interview, you could say either that you find it too personal to discuss and hope they can respect that, or you could even say you have a fear of it being slanderous and would rather not say more. You can try to get away with not saying why, and just say there were issues of a personal nature that you feel you can't discuss, and hope they'll take that as sufficient. The longer your work record, and the better it looks, the easier it is to deal with one bad situation like this.
BTW, the last job I left rather suddenly did not have the owner's name in the company name, but it was a well-known family business in the area, and I didn't have to say any names. But still -- I did try to say some minor things without getting too terribly negative and without blaming some person in particular. Not long later, they went out of business, so it was much easier to just say they were going down the tubes and I wanted out before they took me with them. :-)