When it comes to serving, I've run into four roadblocks that just don't seem like they should be bad things at all.
1. Bisexuality - Being a bi male is a major turn off for some women (just as it's a major turn on for others). I'm not exactly sure why, other than it seems that some women feel that bi men are unsafe, not masculine, or just unsavory overall. I've never been given a really clear explanation, just a cold shoulder once this comes out. It's enough to make me want to hide this, but I don't.
2. Feminization - Even if it's not my "bread and butter," it still just turns some men and women off that I've ever worn panties in my life. This just pushes a button labelled "STOP" when I talk to them. Once they know I've been feminized they don't want to talk anymore. Again, this seems to talk to the "not a real man" idea. Apparently it's okay to be treated like a footstool or ashtray by some people, but not while wearing panties.
3. Switching - Again, straddling a middle line seems to put some people off. This goes for both Dommes and subs. Somehow, having had experience on both ends of the whip puts some people off. To me, it makes my experience richer. To others, I'm indecisive and likely to "top from the bottom" or "bottom from the top". I know my place when it comes to a scene and don't switch in the middle of things but that's just not good enough for some people who feel that once you're on one side of the D/s divide, you should never cross over that big slash.
4. Friendliness - Believe it or not but I've been told on a few occasions that I'm "too friendly to top" -- as if guys need to be a little bit of a jerk to be a "challenge". I honestly don't think that "friendly" in this sense should be taken to mean "creepily stalkerish". I just don't think that's me.
I suppose that "friendly" can be substituted with "agreeable" and one might get closer to the heart of the issue. I enjoy D/s and open myself to new challenges as much as I can. This gives me kind of a carefree attitude. Additionally, I talk to people like they were human beings -- trying to stand on even ground before the power exchange begins. By doing so, I seem to make friends more than making Dom/me or sub relationships. It's a very strange thing to be called "too friendly."