Something borrowed

Elizabeth felt herself growing more angry every moment; yet she tried to the utmost to speak with composure when she said,—
“You are mistaken, Mr. Darcy, if you suppose that the mode of your declaration affected me in any other way than as it spared me the concern which I might have felt in refusing you, had you behaved in a more gentleman-like manner.”
She saw him start at this; but he said nothing, and she continued,—
“You could not have made me the offer of your hand in any possible way that would have tempted me to accept it.”
Again his astonishment was obvious: and he looked at her with an expression of mingled incredulity and mortification. She went on,—
“From the very beginning, from the first moment, I may almost say, of my acquaintance with you, your manners impressing me with the fullest belief of your arrogance, your conceit, and your selfish disdain of the feelings of others, were such as to form that groundwork of disapprobation, on which succeeding events have built so immovable a dislike; and I had not known you a month before I felt that you were the last man in the world whom I could ever be prevailed on to marry.”


(borrowed from Page(s): 214-215, Pride and Prejudice (Barnes & Noble Classics Series) by Jane Austen and Carol Howard, Barnes & Noble, NOOK Study version)


I almost received a proposal on my 19th birthday, before I came to my senses and realized that I was far too young.  I'm pretty sure I still am.  We had been discussing it, and I suspected that it would happen on my birthday. So I broke up with him a couple of weeks before my birthday.  I don't remember how I did it, but it was most likely not as eloquent as Elizabeth Bennet's speech.  Although that level of disdain probably wasn't necessary in my case. I still think, however, that this is the best shootdown of a marriage proposal ever. The last bit is gold if you really want to get your point across.


Jane Austen accepted a marriage proposal, for a day, before she too came to her senses and realized that, although the gentleman in question was a friend of the family and that marriage to him would mean financial security for herself and said family, that they really would not suit each other. I picture her reply to be more in line with this letter written by Charlotte Bronte in response to a marriage proposal from the brother of one of her friends:


My dear Sir
Before answering your letter, I might have spent a long time in consideration of its subject; but as from the first moment of its reception and perusal I determined on which course to pursue, it seemed to me that delay was wholly unnecessary.
You are aware that I have many reasons to feel gratified to your family, that I have peculiar reasons for affection towards one at least of your sisters, and also that I highly esteem yourself. Do not therefore accuse me of wrong motives when I say that my answer to your proposal must be a decided negative. In forming this decision — I trust I have listened to the dictates of conscience more than to those [of] inclination; I have no personal repugnance to the idea of a union with you — but I feel convinced that mine is not the sort of disposition calculated to form the happiness of a man like you. It has always been my habit to study the character of those amongst whom I chance to be thrown, and I think I know yours and can imagine what description of woman would suit you for a wife. Her character should not be too marked, ardent and original — her temper should be mild, her piety undoubted, her spirits even and cheerful, and her “personal attractions” sufficient to please your eye and gratify your just pride. As for me, you do not know me, I am not this serious, grave, cool-headed individual you suppose — you would think me romantic and [eccentric -- you would] say I was satirical and [severe]. [However, I scorn] deceit and I will never for the sake of attaining the distinction of matrimony and escaping the stigma of an old maid take a worthy man whom I am conscious I cannot render happy.
[…]
Farewell—! I shall always be glad to hear from you as a friend –
Believe me
Yours truly
C Bronte


(borrowed from Brainpickings.com and Charlotte Bronte)


Of course, while I should maybe memorize these examples, there's really no need. Any man smart enough will know that I will be the one proposing.  He'll also know not to expect it.