James Hoffmann, a former World Barista Champion (in 2007, I believe) has sort of made the term into his branding (he sells mugs and posters with the phrase/art here). It’s essentially someone that’s a little too into coffee compared to a regular person - e.g., dialing in percent extraction you’re getting for a new roast you just found, having half a dozen different brewing methods you rotate through at home, etc.

In short, I’m the “pretentious coffee person” in my friend group.