First, if you are not interested in buying a pin or don't care for it in general, no need to post your opinion in a FS thread. Etiquette says don't post it in the fan/club thread either. Other threads are open game for posting your valuable opinion. Just because you have one doesn't mean you have to share it.
Equally important to keep in mind, once you have posted your opinion, refrain from making five, ten, fifteen or more posts in the same thread with the same message. Nothing more irritating than hearing John Q Public's rants over and over again. Once the level of posts reaches a certain level of repetitiveness, anything you say becomes noise pollution. Post it once, say everything you mean and then move on.
This has been your public service announcement - be nice and play nice.