Actually - it could be easilly caused by the very same player who blamed you - the White Mage / Healer. Not every Healer knows (or even cares) that over-healing is bad as it takes over the enmity and based on your description of the events you were trying to take it back when lost so simply don't worry - you'll encouter some jerks here and there when using Duty Finder but that's the "tax" for the comfort. As tank you'll have minimum troubles to find another party right away if the situation get really bad and some one will rage quit on you. Don't let anyone to upset you - after all it's a game and we play to enjoy it not to worry.

@Seezur: Your sig always makes me chuckle when I encounter your posts here in the forum