Someone who assiduously builds himself (it's usually a him) up as a social media expert with copious blog posts, tweets, et cetera that cite what the genuine innovators have done, and adds on a layer of jargon and marketing speak in the hope that clueless brand manager types will hire him as a consultant, and similarly ignorant media will think of him as an expert. (The latter is likely, because media types tend to have take the 're' out of 'research' and hit Google, and the SMC will have ensured high rankings by linking to — and being linked back to reciprocally by — other SMCs.) If either of these things happen at least once, he will then post/tweet/status-message it to all and sundry. Over time, he starts to believe it himself.
The only people more boring than SMCs are SEOs.