I wear one lapel pin at a time, if I wear one. Which one I wear tends to depend on the situation, and whether or not I am representing a particular group. For example if I am representing the Scottish Tartans Authority or in another situation where I will be discussing tartan, I wear my STA pin.

I have several pins I have received for service to my church, and I tend to wear one of those on Sundays.

But my hard and fast rule is one at a time. Otherwise I look like a pincushion!