I prefer to be open about things. I see nothing shameful in saying I am bipolar and have SAD, and I wouldn't see anything shameful in admitting I have an ASD, were I diagnosed with one. If someone else does - it's their problem.
Frankly, if a person can't handle the fact that one has issues (of whatever sort, not just ASD), and thinks that anybody with such issues is a second-rate human being, I think it isn't worth having this person as a friend. So nothing too upsetting if they go. Somebody who is a real friend wouldn't have minded in the first place.
I don't think I've had any problems with my friends because of this. I'm usually very frank with them (that, or I'm completely silent), and tell them about anything I feel, so it makes no difference whether they even know I have some sort of diagnosis or not (though they do know). Even without this, they'd have a good idea about what I'm like, how I see the world and what sort of difficulties I have. I don't see the point of friendship - real friendship - if you don't share all these things.
Other people may be put off or not right from the start. Pretty much everybody agrees that I'm "strange" and stand out, again without my ever telling them anything, so some may begin to avoid me after having seen me a couple of times. But I don't mind. Those who can become friends later on always stay.