Okay... here goes.
"...You served us loyally, it's true... but Varys tells me that your brother rode with Renly and then Stannis, whilst your lord father chose not to call his banners at all and remained behind the walls of Stonehelm all through the fighting... Even so... Renly, Stannis, Joffrey, Tommen... how did he (Ser Donnel) come to omit Balon Greyjoy and Robb Stark? He might have been the first knight in the realm to swear fealty to all six kings... It's not Ser Donnel the Constant who concerns me. It's you... What will you do if brave Ser Donnel gives his sword to yet another?... It happened to me... You have no answer?... Good. Return to your duties... and tell Ser Donnel to add a weathervane to his shield."
I think this one is very manageable. Just look to the clues. Look at the context.
I'm going away for the weekend, I won't be back until Sunday evening... so whoever gets it, just go ahead and post another quote.
And I just love the Ser Donnel the Constant and the weathervane remarks.