An API call would go to steemit from an external source, but what I'm describing probably cannot be achieved by anything other than steemit server side, essentially something along these lines (and please excuse the faux verbs/functions):

FOR user submitting a comment, return an array of comments,datetimestamp WHERE datediff(now,12H) AND string(exact(comment)), count all perfect matches of current comment, return count, time, string

user, this is the count time you have posted the exact phrase "string" in time, please consider a less generic response, steemians thrive on original content & meaningful contributions, proceeding with this comment may negatively impact your reputation.
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EG:
copypastamasta, this is the 11th time you have posted the exact phrase "good post, I upvote please upvote me" in 37 minutes, please consider a less generic response, steemians thrive on original content & meaningful contributions, proceeding with this comment may negatively impact your reputation.
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Not something within your purview, I know, more just a hypothetical item for discussion.