What is the best way to tell your unit that you in no way shape or form want an ETS award from them?

Oh, this needs to have a story time to enlighten us as to what is up. But to answer your question, there are many routes you can take. You can do the extreme direct approach and not walk up to the Commander when called. Or, you can walk up and THEN tell the CDR to their face you don't want it. You could walk into your 1SGs office and state your case. Or, you could run the request up through your TL/SL/PSG and have them relay that request to your 1SG. OR.....and just hear me out.....you could simply take the award when it's presented.....ya know, be that NCO that sets the example....then about face and drive on with your life. Because in the end, if you take any of the options that were listed prior to the just taking the award and moving out, then you could set the bad example to the rest of the Soldiers (especially the Junior Enlisted) within the unit which could then in turn create even more issues within the unit in regards to morale and discipline. I would gather that you have a rather bad taste in your mouth for your unit and probably the Army as a whole, but remember this.....until that ETS date rolls around, you are still in the Army and you are an NCO. Operate as an NCO.

Hmm....
I would say "Suck it up and take the award, you may not appreciate the award right now BUT you or your children might some day in the future."
My father passed away when I was 11 and served in the Army some 20 years prior to my birth in a time (1950's Germany) when all you could basically get for awards for service were for acts of Heroism or a Good Conduct Medal. To commemorate his short military career all we have is a few pictures and a DD214 (with the awards block blank). Based on the DD214 and some second hand info from my mom all I basically know is his MOS and his UNIT. I do not even know which MOS was his primary and which was his secondary, I just know, he made it to SP4, and had been to Fort Dix for Basic, then Engineer School @ Fort Belvoir for "Engineer Equipment Repairer" and then Aberdeen Proving Grounds for "Welder Blacksmith School." then sent to his unit in West Germany. He was discharged from Active Duty just shy of 3 years "because of transportation back to the United States" (re that is when his troop ship sailed, it was serve maybe another 3 to 6 months on active duty OR get discharged "early") An ETS award probably would have told me a lot more than I was able to figure out about him from the DD214, more such as exactly what he did in his unit (an "Engineer Detachment") or what his detachment did. Did he just fix the machines of did he ever get to operate them? (He ended up as a civillian Operating Engineer in the International Union of Operating Engineers) was he good at his job or really good or just average? Was he a squad leader? When they went to the range did he consistently qualify on his assigned weapon? Sometimes ETS awards I have seen include all of this stuff and it tells the family a story. I wish I knew more about my dad' short Army Career, don't let your children be left scratching their heads because you refused an award. I am currently sending away for his Cold War Service Certificate.
Don't let an award slip through your fingers when you could have had one, it will be something not just for you but for your family. It will be something for future generations to record your history.

****warning.....this is horrible advice******
get flagged...

****this is good advice******
write yourself a nice little AAM. Steal the format from a recently approved one, and say thank you to those you served with.
The award is not really for you. The award is for your family and future grandchildren to look back on and be proud of you. Don't take that away from them.