What advice can I give a friend who admits that he purposely fails his promotion?

I recommend one of two things:
1. That he start taking his military career seriously (and putting his best efforts toward getting promoted), or
2. That he update his resume and start looking for a civilian job.

I guess I would have to ask.... Why?

Is it a question of competence (or perceived competence)? Responsibility? Time/commitment?

There are lots of valid reasons to turn down a promotion NOW. There are not a lot of valid reasons to turn down promotions long-term. For a young Soldier planning on an active duty military career, the number dwindles down to 0.

Here's the thing. He isn't fooling anyone. Either he is screwing up so badly and so consistently that those 1SGs now believe he is totally incompetent, or he is screwing up in such a manner that the 1SGs think he is competent but a jackass. Either way, he is demonstrating to those 1SGs that not only is he not ready to lead Soldiers, but he also is not ready for ANY responsibility - to include the responsibility of schools, TDY, moving out of the barracks, or even staying in the Army.

I have met a lot of senior NCOs who were not particularly bright. But very few who couldn't see through BS. And NEVER a group of them, like you see on a promotion board. And every single promotion board I sat on, we DEFINITELY discussed the candidates before and after their appearance.

Your friend is setting himself up for failure not just now, but for months to come. If not years.

I've seen a SM be SPC for a decade - just had no desire to be an NCO or lead. It's his career. At some point RCP will get him and he won't have to worry about the board any more. If he does wish to continue to servie then he will need to show some interest in passing the board and moving up.

SFC Casey O'Mally described it the best. I was once a specialist myself. Is this the first actual career or job outside of high school? He may have some personal issues or depression and maybe he needs to talk to the chaplain?
If he is a smart guy who just purposely wants to Foxtrot everything up, then he needs to do his best until his enlistment is up. Can you imagine getting in trouble and getting and other than honorable discharge? Maybe it won't come to that. I guess the Army resiliency training slides don't apply to him? Right before I retired, I worked with the assistant G3 in my one-star command and he wrote this up on the easel and I was very impressed by it! If he doesn't go by what was written in this picture, then he needs to get out of the army under honorable conditions.
A1C Medrick "Rick" DeVaney MAJ (Join to see) MSG (Join to see) Sgt (Join to see) SFC Casey O'Mally LTC Kevin B. SGM Jeff Mccloud

What LTC Kevin B. said!

What advice can you give? Just simply tell your friend that they either better get their best Army Foot forward if they want to stay in the military or start getting their resume written up for the upcoming civilian life. I'm kind of surprised your friend hasn't been given a Bar to Continued Service. But, as soon as Command catches on, that Bar will be put in place.

Basically, you need to tell your friend to shit or get off the pot.

SGT (Join to see) We should all strive to push ourselves out of our comfort zones. Promotions in the military are something to look forward to along with the increased responsibility that comes with it. Promotions help us grow as individuals and enable us to tackle harder challenges that we will face in the military and civilian world.

Eventually he will hit the up or out ceiling: Retention Control Point. Although RCPs have recently been modified, in order to have hopes of retiring he needs to make SSG in order to make it to 20 years, as SGT faces RCP at 14 years.
In my experience, some soldiers just don't feel comfortable taking on higher levels of responsibility. Particularly where they have to direct others. They like what they are doing where they are, and want to keep things as is. If that is the case, as he gets near RCP he should follow advice already posted about readying himself for another career path.

If you think he may be subconsciously failing, or failing unintentionally because of fear, then help him get to a mental health counselor or Chaplain.

If he gets out before retirement because of non-promotion, thank him for his service and encourage him to see Veterans Affairs for further assistance.

this person doesn't want any advice.

Ya gotta be there to comment. He may be dumb, or smarter than you think. One of the advantages of the military life I recognized, is that within limits, you can select how responsible you need to be, depending on several factors. You can be comfortable being a little fish, if that suits your needs. I was able to turn down a promotion at just the right time, for excellent reasons in my case. Still approve the decision. Maybe he felt he needed to wait for greater maturity before advancing, or just didn't feel up to the challenge (think: Peter Principle). In that case, if he really was capable, a little encouragement could go a ways.

I had to make a similar decision during my civilian career, in my particular circumstances. Also was best for me.