It sounds like the Finish Military may be a bit different than the US Military. The fact that you are encouraged to wear civilian clothes is odd if you are a contract member of the military. I'm interested to understand why this is.

If you have the right to meet with the higher officers in your chain of command, that should be your first step. If you get their approval, this guy can take a hike and you will have his superiors OK. However if you make this a personal confilct between you and the officer, the higher command may decide that enforcing discipline is more important than what the dress code say's.

Plying graba$$ with the military in the US is not a game you will win usually mainly due to the fact that they OWN you for the term of your contract.

Do this with respect for yourself AND respect for your service and things will worjk out a lot better. Make it a personal attack on an individual officer and your odds of winning drop off greatly.