Hello Arush: I see this is your first post here on PC. So... welcome to PsychCentral!

I'm sorry I don't think there is going to be much I can tell you about this. I'm not a mental health professional. However, my understanding of fetishes is that they are generally related to sexuality. From what you wrote, it doesn't sound as though there is anything of a sexual nature to what your son is doing. So perhaps this more related to his OCD condition? This is really something that would have to be determined by a mental health professional.

You asked if you should talk to your son's therapist. Since your son is an adult, & assuming you are not his legal guardian, his therapist should not talk with you without your son's approval. And since your son gets angry when you ask him why he does what he's doing, it seems unlikely he would give his therapist permission to talk to you. Consequently, talking with your son's therapist may not be an option for you regardless of whether or not it might be of benefit. If your son will give his permission for this to occur, I don't think it could hurt; although I don't think you should probably go into it expecting that it's going to result in much of anything specific either.

The impression I have, with regard to fetishes, is that they are devilishly difficult to break. The general consensus of opinion seems to be that the best approach is simply for the person who has one to indulge their fetish as safely as possible. As long as the fetish isn't harming the person who has it in some way, or someone else, then having a fetish is not generally considered to be a problem. And whether or not what your son is doing could or could not be classified as a fetish, it may be necessary to look at what he's doing in this way. If it's not causing some significant harm, in some way or another, then it's not something to be concerned about.

What may be of more significance is the fact that your son is still living at home (although I don't know as that is necessarily unusual nowadays either.) And then the other potential area of concern may be with regard to whether or not he has a job or is in school... that sort of thing. If your son is living at home, has no job or other types of activities (volunteer work for example), is not going to school, & just spends all of his time by himself stuffing his undershorts with teddy bears & pillows, then of course this certainly is something to be concerned about. However, as I indicated above, I doubt this is all something you're going to be able to talk with his therapist about unless your son will give his permission for your therapist to talk with you.

Knowing so little about your situation, it's difficult for me to say much more than this. Ultimately, I think what you are perhaps going to need to focus on is are you comfortable having your son continue to live with you & does he have, or is there in some other way, a plan for his future. From that perspective, to my mind at least, the fact that he'll only wear one type of undershorts & the fact that he stuffs them with pillows & teddy bears, while it certainly is odd behavior, is probably a side issue, so to speak. At least these are my thoughts with regard to your post. I wish you well.