I stay away from spoilers best as I can, too, but the whole staying offline till I've seen it doesn't really work when it's Doctor Who season 4 we're talking about, which won't be airing till March or April.
I go about cutting spoilers in that way that I put all spoilers about un-aired episodes behind a cut, and then anything that's more detailed. Like, I wouldn't cut something like, 'Omg, in SGA 4x17 Ronon tickles John's ear!', but as soon as I start talking about major plot points or things that would really spoil the fun for someone who hasn't seen it yet, I put it behind a cut. Mostly I'd do that even without considering the spoilers, because chances are it'd be a tl;dr ramble xD.
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I go about cutting spoilers in that way that I put all spoilers about un-aired episodes behind a cut, and then anything that's more detailed. Like, I wouldn't cut something like, 'Omg, in SGA 4x17 Ronon tickles John's ear!', but as soon as I start talking about major plot points or things that would really spoil the fun for someone who hasn't seen it yet, I put it behind a cut. Mostly I'd do that even without considering the spoilers, because chances are it'd be a tl;dr ramble xD.