Can’t say I’ve come across it being used here instead of atheist. Paganism is a form of worship as far as I believe so it wouldn’t be an accurate description.

Is Christo-centric a word? You know, looking at the world through the Christian perspective. And 'infidel' must mean 'unfaithful' or maybe 'not faithful' to Islam. I'm not sure what 'heathen' means. I really like the way English has so many ways of expressing ideas that are close but not the same. And I think we always have been too lazy to use them properly.

I don’t use it, and have considered it a method of demeaning atheists. Sounds like a religion unto itself..

I think current usage is hazy, if not lazy. But @Matias provides, as usual, the historical perspective. Self-described modern pagans in my experience are Wiccans or animists of some stripe or other. Worshippers of nature, basically. The term doesn't carry a negative connotation to me.

Pagan:

noun

1. One of a people or community observing a polytheistic religion, as the ancient Romans and Greeks.

2. One who has little or no religion and who delights in sensual pleasures and material goods: an irreligious or hedonistic person.

Conclusion:

A person partaking in an orgy, while being observed and judged by multiple gods.. and is also wearing very expensive jewelry.

Certainly, there are lots of beliefs which could be called pagan which are all quite distinct. Old European pagan is different from North American Indian beliefs. I certainly prefer it when people are specific about what they mean.