Honi soit qui mal y pense

Old French, translates to Shame to him who thinks evil of this. The motto originates with the Order of the Garter, and appears on the British Coat of Arms. It's considered a reiteration of God's words to Abram: "I will bless them that bless thee, and curse him that curseth thee." (Genesis 12: 3)

Apocryphal origins of the phrase
At a ball, Joan Countess of Salisbury lost one of her garters. Seeing her embarrasment, King Edward III retrieved it, bound it to his own leg and rebuked onlookers by saying, "Honi soit qui mal y pense." Inspired by his act of chivalry, King Edward founded the Order of the Garter in 1348.

Isn't Honi supposed to be written Honni?

Well, yes and no. In 1348, the spelling was honi. But, like most languages, French evolved and today the double N is the norm in the French language. Henriette Walter wrote a book documenting the 'love story' between the French and English languages. It is aptly named "Honni soit qui mal y pense" (note one of two 'n' is italicized)

Source: http://www.rfi.fr/Kiosque/LangueFrancaise/EntrevueAvec/05032001-0.html interview with Henriette Walter