Should I try to talk to my parents again before I come out publicly? They didnt listen last time I tried to tell them...

Have your parents sit down. Turn off the TV and don't open the door to anyone who rings or knocks. Remove the phone from it's hook. You don't want any interruptions.

Plan what you want to say. Take notes to what the typical questions parents may ask. Search the internet. You will have to let them understand you know what you are talking about.
Let them know how many years you have felt this way. They need to know this is a firm and solid decision you have made on your own and NOT a passing fad.
Allow them too what restrictions they may have. (i.e.)You shouldn't be seen with your girl friend in public if this is their request. Not be seen where their friends will see you.
Most of all research the possibilities in diseases from multiple partners. If they know how informed you are, you will have a better audience. Take your time and be thorough and concise.

I had read the suicide rates of young adults who contemplated Suicide rather than telling their parents and initiated this 'talk' on my own.
They laughed and told me, 'No way Mom.' But I know I opened the window to be there for whatever life threw at them.

Ummm... honestly? Why do your parents need to be involved in your sexual identity at all...? Don't make a big deal about it. Just be YOU.

I'm just trying to figure out why this would be an issue. I never had the urge to involve my parents with my sexual orientation-- because, fact is, IT'S NONE OF THEIR BUSINESS.

You've already told them. Are you looking for an endorsement...? Why is it so important that they are a part of your sexual identity?

Well i would tell them again and then just live your life they will come around in a few years, just remember they will have to deal with "grief" and everyone handles that differently, a good thing would be to google "Grieving Process" it may help you understand them and the way they are thinking and good luck :)

Talk to them one more time. Make yourself be heard. If you have to shout it out while standing in the kitchen, then do so. Tell them that this is you respecting them because you wanted to discuss this with them before you come out publicly - and you do intend to come out publicly! The 'put-off' that they are exhibiting is them not wanting to face reality and the fact that you know who you are and seem very comfortable with yourself.

Give them one more chance. If you feel you are still being put off, do what you must. Good luck!