@PCutter I don't know if you were right, but I think I know how you can find out. At least, I hope so.
See, I believe there are cool ponies who respect others and not-so-cool ponies that don't. In order to live a happier life, I rid myself of the negative influences around me (those people who said they were my friends, but were really were in it for a one-way relationship; "one-way" meaning theirs). If you think A is one of these, and you don't feel comfortable with them, then I say wish them well and walk on. Hold no hate, but do cut off the relationship. If this person has some kind of perspective that says "anyone who doesn't hate Pinkie Pie is a jerk!" then they have drawn a line. And that line might cost them friends. Including you. But, it's their decision. You appear to have had nothing to do with it.
On the other hand, if there is more to the story than this, and this is all just a misunderstanding of some kind, then I recommend by all means, sit down with them in a place of no distractions and, in a civil, respectful way, get to the bottom of it. If A is really your friend, A will respect your opinion regardless of theirs. Maybe they were just having a bad week? Maybe not? Follow your gut instinct. Trust your feelings on the matter.
If you see it the same way, then you have (what I hope is) an answer to your very important question. Whatever happens, good luck with this!
Honor and fun,
Summer Storm =)
P.S. On a loosely-related note, Pinkie Pie is the entire reason I became a Brony (see my Profile if you want details). =)