No U

The mother of all negative commands and the penultimate command of non-affirmation, which being one of the oldest words of the English language, dates all the way back to Old English. It is composed of simply two letters: The fourteenth letter of the alphabet, N, and the 15th, O. In this context, it is followed by an intentional misspelling for the word that describes a party that is a second-person subject to a direct address by another party, simplified with simply the 21st letter of the English alphabet, namely U. This intentional misspelling is used to express and emphasize the how much ignorance the speaker has in correct English spelling, which is common in the modern Internet world, and therefore, this misspelling is used as a subtle tool of assimilation into the complex society of the Internet. A blank space is traditionally added between the first two letters, N and O, and the last letter, U, most likely to add a non-casual taste to the originally very casual nature of the phrase, by not sounding like a nervous first-time public speaker rushing every single word and constantly putting two words together. Put together, and you have this phrase, the penultimate counter-attack to any hater trying to roast you hard, the remedy to any insult or unpleasant remark you may receive from your "friends".