While I dont have an opinon about the act itself, I do think that acts of refusal, in any context and in whatever way feels important, are ways for us to see ourselves resisting. What I mean is: as anarchists, as persons questioning the norms all around (i.e flag worship, etc..) it seems important to find out where you stand in the world and how you stand there. So, I think resistance towards acts of the mass, ideas of a person you share space with, or anything otherwise presented to you (or imposed upon you) is an overall good thing and way to know yourself and know when to say "no", with or without explanation. And this is where I disagree with Lawrence, I don't think you need "well-thought-out or easily understood reasons" to say no. I think part of being a person is not always understanding the full reasons for why you do something and the interesting part of being a person is learning what those reasons are over time, learning how to better articulate them.
To answer your question of what do I think of you for doing this: great.