I'm not sure about you, but I think being called "human spam" would probably be one of the most interesting yet insulting insults I could receive. When you think of spam, you think of the pesky, annoying, and unwanted junk that fills your inbox (or that nasty ham stuff that comes in a can). No one wants to be human spam.
I think what Austin Kleon means by the term "human spam", is someone who overshares without discrimination of what they're sharing, all the while disinterested in the actual valuable work of others. It reminds me of the friend who only wants to indulge you with stories of their own life without asking you about your own. It's total self-involvement, often without a reason.
Austin Kleon suggests that in order to avoid becoming human spam, you must be an open node. You must stop believing the world centers around your work and engage in the work of others - become more interested and in turn you will become more interesting. The best artists "acknowledge that good work isn't created in a vacuum, and that the experience of art is always a two-way street, incomplete without feedback" (126). Stop glorifying your work and your work alone, and begin glorifying the work of others. It's like our mom's told us: the world doesn't revolve around you!
The theory of human spam begs the question, if we don't promote our own work, who will? To this I say there is a difference between promoting and oversharing. Promoting should involve choosing your very best work to present to an audience. Think of it this way - if a potential employer asked you to create a portfolio to submit for review, you wouldn't include any old half-assed piece of work would you? No. Sharing on social media with your friends should be no different. Just because they may not pay you in the future, doesn't mean they aren't deserving our your very best!