Yes, the per post, similar to the like. I do favor the multiple choices that I have on Talk About Marriage (TAM) and FB. And in my thinking it could be a way by which those who never learned the fallacies, like me, could better become acquainted with them. Oh, especially if the word, if selected, were to be a link to an explanation of the fallacy. I do get that, especially people new to debating, will end up attributing the wrong fallacy to a given argument/post. While the fallacy is clearly defined, what it applies to might not be so. So again, two people could think that the same argument is two different fallacies.
I do get the concern about people using them just for annoying and spamming on others. It was an idea that popped into my head. I know I wouldn't mind being able to point out to a person that they made an ad populum fallacy but not necessarily have to post about it just to say, hey you make this error.