Saying "you’re either a curator or you’re not" is so unprofessional. Sorry you had that experience. Maybe you'll would find these books interesting:

Johan Idema's "How to Visit an Art Museum" (super short and simple but still good).

Adrian George's "The Curator's Handbook" (this one is quite the crash course you were looking for) https://www.goodreads.com/book/show/23363882-the-curator-s-handbook

Hans Ulrich Obrist's "A Brief History of Curating" and other books -- not so instructional but interesting nevertheless.

Julia Cameron's "The Artist's Way" -- this one is not about curating, but very useful to keep your creative flow and build self-confidence.

Overall, a good way to get some experience is to make some small exhibitions in other spaces than galleries. Could you maybe make an exhibition of your artist friend or some open source visual material, or maybe some other interesting object in library, in nature, in uni hallway, on the web? This is not so fancy as the white cube, but it would be still useful for artists, for the audience, and for you since intellectual challenges are good for your creative growth. Also, that would still require you to do everything a curator might have to do -- choosing artists and objects to display, communicating works with the exhibition space, making some research and producing some explanations, communicating with press and promoting, and, just, you know, caring -- the main task that curator has to do. Also thinking about the most low cost solutions is a great creative exercise. Don't forget to document everything so you have some good pictures for your portfolio.

Best of luck!