The very definition of religion (or being religious) is a mixed bag. Whether we are talking about being religious in brushing our teeth every day or in believing and practicing religious dogmas, religion itself has a very broad range.
But more specifically, since we are in the Religion subforum, and assuming that we are referring to religion in regards to the supernatural, the answer is pretty simple.
ULTRA here claimed that nobody decides. I think quite the opposite is true. Anyone can decide whether or not someone is religious, regardless of if it is themself or others. Traditionally, religion - or being religious - was thought of as someone who simply believed a supernatural teaching (such as Christianity, Islam etc). No practice or ritual was necessary to represent their beliefs. However, more recently, a new term has come into light: "Spiritual". In previous history, "spiritual" and "religious" were, in definition, one in the same. Yet, in modern society, we find that though the defining characteristics of being "religious" has slightly more or less stayed the same (meaning to belief), being "spiritual" has somewhat taken on it's own meaning.
It seems that with the changing times, being "spiritual" has come to identify someone who believes, and being "religious" means to take a proactive stance in their beliefs - to practice the rituals associated with that belief system.
Now, understanding that the two are different in contents, the definition of being "spiritual", in my own observation, has also come to mean that the believer is more moderate or passive in their belief and practice. Whereas, the "religious" are more stern and adherent to their religions teachings, regardless of their own personal mentality or judgements against their teachings.
I've said this before somewhere on this site, but cannot recall exactly where. Regardless, I still find that the following phrase, though different in structure, can apply to this discussion:
"Morality is doing what is right regardless of what you're told. Religion is doing what you're told, regardless of what is right."
It seems very simple that, by abiding by the definitions as I have provided here, one could seemingly replace "Morality" with "Spirituality" (so that I am clear, the two are unrelated and I do not mean to replace one with the other to mean the same thing in it's own definition. Morality does not equal Spirituality. I'm simply changing the words to show that typically the people who are "spiritual" tend to be more lenient and moderate in their belifs. I.E. Being "spiritual" does not, in essence, require the same adherence and practice as being "religious".)
Now, as I digress, anyone can be either religious or spiritual by the their own consideration or that of others. We need no authority to designate who is and who is not one or the other. We are able to discern that on our own, based on our own interpretation.
I hope that what I've said here is understandable. The definition of who is religious (or spiritual) is really a subjective pretense which can be applied to anyone.
