Still, I didn’t want to respond with “I’m from Durham, North Carolina, a predominantly black southern city and y’all are white fools for thinking “sheeeee-it” is something new,” as I’m in fact from the suburbs of Durham and am myself half white(/Asian), but as I was reading Jack Kerouac’s On The Road last night, I stumbled across the word and its particular pronunciation three times in the space of a page (200):

Yah, what’s good’s a ball, life’s too sad to be ballin all the time, said the tenorman, lowering his eye to the street. “Shh-eee-it!” he said. “I ain’t got no money and I don’t care tonight.”

…

We saw a horrible sight in the bar: a white hipster fairy had come in wearing a Hawaiian shirt and was asking the big drummer if he could sit in. The musicians looked at him suspiciously. “Do you blow?” He said he did, mincing. They looked at one another and said, “Yeah, yeah, that’s what the man does, shhh-ee-it!

…

The big Negro bullneck drummer sat waiting for his turn. “What that man doing?” he said. “Play the music!” he said. “What in the hell!” he said. “Shh-ee-eeet!” and looked away disgusted.

Not to suggest that On the Road premiered the term, but it does offer proof beyond the anecdotal that the elocution is (at least) fifty years old. So there you go, Slate folks: it ain’t nothin’ new. Sheeee-it.