I think the confusion comes from "intentional" suggesting the player actually intended to commit the foul, as opposed to simply too much force. Shoot, if we could really read minds, half the fouls would be intentional!
As for mechanics, I've never called a flagrant foul, but I suppose the crossed arms are simply followed by the ejection signal used in baseball (without the full body motion, of course -- after all, we do our jobs without any sign of emotion
).