How should I proceed if it's pretty clear that a colleague is showing behaviors of Asperger's but he has no clue and it's very frustrating for those that work with him. Especially me because I'm his go-to guy.

His manager brought up to me the possibility that it's Asperger's and its description fits the guy very well.

Now what? Nobody's bringing it up to him and while I ask him to change the way he approaches me, he just keeps up the behaviors. His manager seems reluctant, as he is generally reluctant to manage and is just looking toward retirement.

I feel really stuck with this and the guy's behaviors pop up almost daily.

What should be the first step toward dealing with this situation?