Can a civilian give a challenge coin?

Can a civilian really give a challenge coin? I've always thought that challenge coins were exclusively for military personnel to exchange as a sign of camaraderie and recognition of service. But I've heard of civilians gifting them too. Is this an acceptable practice? If so, what's the proper etiquette around giving a challenge coin to someone outside the military? Are there any specific rules or customs that should be followed? I'm curious to know more about the tradition and how it applies to civilians.