The only story with a barbed cat-like penis I know was a Kirk/Spock one, though McCoy has a large role as Kirk's friend, but otherwise it fits your description: Secret Vulcan Mating Rituals by Chase820
Since I actually searched here in this comm for other fic in which Spock has a cat-like penis after reading that, and got no replies, I think you might be mixing up the K/S with a Spock/McCoy one.
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timeasmymeasure
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Date: 2010-03-02 07:50 am (UTC)Since I actually searched here in this comm for other fic in which Spock has a cat-like penis after reading that, and got no replies, I think you might be mixing up the K/S with a Spock/McCoy one.