Tutnese

Tutnese or Double Dutch is a language game primarily used in English, although the rules can be easily modified to apply to almost any language. Tutnese is usually used by children, who use it to converse in privacy from adults; by members of historically marginalized minority groups for the same reason when in the presence of authority figures such as police ("pupolulisus" or "pizolizice"); or simply for amusement and humor.
Language rules.
In Tutnese, vowels are pronounced normally, but each consonant is replaced with a syllable from the following table:
Double letters in a word, rather than being repeated, are preceded by the syllable "squa" to indicate doubling. For doubled vowels, the prefix becomes "squat" instead—thus, "OO" would be spoken as "squat-oh".
Word Example: "Tree" becomes "Tutrugsquatee". 
Sentence Example: "I took a walk to the park yesterday" becomes "I tutsquatohkuck a wackalulkuck tuto tuthashe pubarugkuck yubesustuterugdudayub".
While spaces between words are always ignored, at least one "dialect" requires that the first syllable of the name of any given punctuation mark be spoken, thus a full stop (period) is 'Per', a question mark is 'Que' ('Kway' or 'Kay', varies), and a comma is 'Com'.
History.
This game appears to have been invented and used by African Americans in the American South, to teach spelling and conceal what they said, at a time when literacy among slaves was forbidden.
Ernest Thompson Seton mentioned it in his book "Two Little Savages." Yan, the hero of the book, learns it and tries to teach it to his friends Sam and Giles, but the other boys are not interested.
Maya Angelou mentions learning Tutnese as a child in the first volume of her autobiography, "I Know Why the Caged Bird Sings". She and her friend Louise "spent tedious hours teaching ourselves the Tut language. You (yack oh you) know (kack nug oh wug) what (wack hash a tut). Since all the other children spoke Pig Latin, we were superior because Tut was hard to speak and even harder to understand."
There is a version used in some parts of the US called Yuckish or Yukkish, which uses more or less the same constructs.