Enjoy. Little warning: Some of this refers to roll XdY; if you don't know, this is a P&P RPG mechanic which means roll X Y-sided dice.
1. Roll 1d20. On a roll of 20, write the post entirely in caps and skip step 4. Otherwise, proceed normally. Note that some boards use a filter to block out messages in all caps. You can get around this by replacing an "I" with a lowercase "L." Most typefaces show these identically.
2. Write out your post in its entirety, using proper grammar, spelling, and punctuation.
3. Now, go back and edit your post. First, delete all commas, semi-colons, colons, apostrophes, hyphens, dashes, parentheses, and spaces after periods.
4. Roll 1d3. On a roll of...
----1: Make all letters at the beginnings of sentences lowercase, but keep all proper nouns and adjectives capitalized (unless they're at the beginning of a sentence).
----2: Make all letters at the beginnings of proper nouns and adjectives lowercase, but leave the first letter of a sentence capitalized (unless the sentence begins with a proper noun or adjective.
----3: Make all letters lowercase.
5. Starting with the first word of your post, roll 2d6. Count that many words into your post to find the next "Target Word." For each Target Word, roll 1d4. On a roll of...
----1: Reverse the order of the last two letters of the word.
----2: Delete the space immediately after the word.
----3: Select a vowel in the word and replace it with another vowel of your choice.
----4: Select any letter in the word and replace it with another letter that is found on a neighboring key.
Repeat this until you reach the end of your message.
6. Run the spellchecker. For each word that comes up, roll 1d3. On a roll of 3, replace the word with an incorrect suggestion. Otherwise, leave it alone.