I would approach furs the same way I'd approach religion, unusually gleefull rights, abortion, and any other view where the "moral" thing to do would be to convince as many people as possible to believe the same thing you do (whichever side of the debates you're on). Weigh the costs of speaking up against the costs of this particular person not believing in your cause, factoring in the chance of them actually being persuaded by your argument, and either speak up or don't.
I've had vegetarians get in-my-face about me eating meat. My aunt refuses to eat in a restaurant that also serves meat (which at first meant we all changed our dining plans, but now means she gets left at home if she makes a stink). I've also had a friend give me a well-reasoned argument about why he chooses not to eat meat, especially pork, and I found I agreed with him on some points. While I still eat most meat, and don't have a moral problem with it, I now avoid pork and ham for environmental and economic reasons (at least, when I have a choice, I choose to eat something else instead).
There *is* a way to evangalize properly, be it religion, politics, or saving the spotted owl. Annoying people ain't it.
ETA: lol, "g a y" is changed to "unusually gleeful" on this forum.