Hashtags at their best stand in as what linguists call “paralanguage,” like shoulder shrugs and intonations.
That’s fine.
But at their most annoying, the colloquial hashtag has burst out of its use as a sorting tool and become a linguistic tumor—a tic more irritating than any banal link or lazy image meme.
The hashtag is conceptually out of bounds, being used by computer conformists without rules, sense, or intelligence, a like yknowwwww that now permeates the internet outside of the tweets it was meant to corral. It pervades Facebook, texting, Foursquare—turning into a form of “ironic metadata,” as linguist Ben Zimmer of The Visual Thesaurus labels it.
via How the Hashtag Is Ruining the English Language (Updated).