Any ideas for how to teach a subordinate E-5 tact?

better do it now than later

He has to learn on his own, or you could tell the NCO you get more from honey than you do with vinegar and that respect goes both ways

The fact that he is promote able already tells him that there is nothing wrong with his behavior. If his tact was an issue, it should have been addressed before he was ever boarded. That being said, counseling as always. I have ways been a verbal guy, so sit him down and be blunt, explain it. If u need more experience in the room, maybe involve the plt Sgt or 1sg in the discussion. If it doesn't improve, then u have 4856's.

give the Soldier the LEADERSHIP fm and high lite areas of concern in the fm. Tell the Soldiers there are many ways to lead but a good combination of the three basic ones will give the Soldier the understanding of what it means to lead

You need to be direct and to the point. There are multiple aspects of being a Non-Commissioned Officer and if he can't correct his malfunction then take his promotable status away.

Send him to recruiting. That boosted my interpersonal skills through the roof.

Continuous mentorship and counseling on your part can win the day brother. If you have to pull him off to the side or to another room and spell out what he is doing wrong as you see him doing it. Most of my leaders did that with me and eventually it took hold and I improved. The one thing that you will have to remember as well it that he will not change unless he is made to see that he is doing wrong and needs to change.

First and foremost, understand that tactful communication is an issue of respect. A lot of junior NCOs lose sight of the fact that respect goes both ways and that it can be easily lost by not treating a subordinate with basic respect.

Counseling. Make him look up the word tact because maybe your explanation isn't working. You can also have a squad meeting and let the rest of the troops tell him what he is doing that bothers them. Make sure they have no worry of repercussion from the discussion. Sometimes it is important to just have an informal, no holds barred discussion amongst team members to get a point across. When I was still in I knew plenty of new NCO's that were on big power trips after they got pinned. Another idea would be to make up a situation and ask him how he would handle it. If it isn't the desired result then you show him how it should be handled. It's a tough thing to teach and sometimes you just got to let them fall on their own face before they learn. Being he doesn't have that tact and seems to see things only as black and white then I wouldn't promote him. If he already has that promotable status then there isn't much you can do. Just try whatever approaches make sense to you and hope for the best. Things will come to a head eventually and the senior leadership will fix him if you can't.

Everyone has good comments on this issue. How long has he been an E-5? Was he promoted to E-5 under you?
If this has been going on for a while, he needs shock & Awe treatment. This treatment usually comes from the 1SG. Fifteen minutes with the first shirt and you may start to see an improvement on his part. The respect from others will take time.