The astute among you may have already guessed this is in reaction to an investigator PC using a syringe spear to deliver an infusion of skinsend to an unwilling target.
By RAW, I don't think the target can choose not to accept. Basically, they're under the effect of a Skinsend if struck, although their next round they can take a standard action to dismiss the spell (since they are the "caster," i.e. the unwilling imbiber of the infusion extract). But I'm wondering if I missed something somewhere about whether one has to accept a dismissible personal spell.
And if unable to not accept the spell, the corollary question is: if they dismiss the spell the following round, are they at 1/2 HP, per the spell, or is it as if the spell was never cast? RAW, I think it'd be half hp.
Just trying to wrap my head around this very corner case...