I wound up telling my sister and her girlfriend when we somehow were discussing sexual preferences anyway, because I couldn't help but one-up her worst/craziest thing she'd seen, their reaction basically amounted to 'good for you, but I'm not into that'. I also namedropped gurochan to another (very close) friend once, but I don't think she ever checked it.

I think a big part can also be in the delivery. Explaining guro as 'fetishized extreme violence and death' not unlike an extension of sadism/BDSM, is bound to go less poorly than 'I get off to pics of chicks pissing themselves as they hang to death'.

Personally, I intend to tell my partner when I have one, but few other people (siblings and a few close friends), and only if it somehow comes up.