firecat

Simply not showing up requires a very high participation rate to be effective, albeit less so if if there's some kind of alternate event (not necessarily with a shunned-person-related theme) at the same time. Walking out (quietly and respectfully, of course) at the point that the shunned person is introduced is very visible. For events where attendance is more or less compulsory (commencements come to mind) there's standing up and turning one's back on the speaker, which is very visible but imposes the cost of being there on the shunners. (I've heard about some universities attempting to discipline students for doing this, but my impression is that those disciplinary efforts failed fairly resoundingly.)

For the more highly placed, there's also the cut direct.

(Oh, and I've come to a conclusion -- because that's my privilege as a middle-aged white guy whose last serious fan experience was 30 years ago -- about post-invitation actions by someone who has been invited to an event to be honored. If you know the principles of the group honoring you (and you should) then it's rude to publicly trash those principles and still go. It's like being invited to a vegetarian dinner and announcing that you're going to order in a rib roast.)