Frigorific sounds like a PG version of fanfuckingtastic

That would be an excellent band name.

Why do you think the reason needs to be explained at all? Every site that uses an up/down vote system has pretty clear guidelines on how they are meant to be used, so either the user is voting according to those rules, or is using it as a like/dislike button. Commenting is typically reserved for contributing to a conversation, and in most instances, justifying a vote ends up being either noise, or comes off as complaining about Internet points.