If you want to express your gratitude for someone's kindness, there are many other ways to say "awfully decent of you". Some synonyms include "extremely gracious", "exceedingly kind", "exceptionally thoughtful", "tremendously considerate", "incredibly generous", and "immensely helpful". These phrases convey a sense of appreciation and admiration towards the person who has done something nice for you. Alternatively, you could say "much obliged", "thank you kindly", or simply "thank you" to express your gratitude. No matter how you choose to express your appreciation, remember to do so with sincerity and a genuine heart.