Ask HN: How does a programmer go about learning business?

I was thinking of going into a Master's in Computer Science but, as challenging as that would be, it wouldn't challenge my world view.

I've historically, and very immaturely, held a contemptuous attitude towards business domains and business professionals (sales, marketing, PR, etc.)

I would like to change that by challenging myself to gain more knowledge of these fields. Perhaps even be able to apply them in my life by being a little entrepreneurial in the future.

Thing is, I'd rather not do an MBA. So what are my options?