l33t syndrome: A common disease that infects children, usually male, between the ages of 13 and 17. Symptoms include a propensity to use numbers and misspellings (as well as mispunctuation) in place of proper 'net English, a terrible need to prove oneself, and many other annoying habits that only script kiddies and l33t h4x0R boys (and girls) have.

Example: My learned colleague would have presented a compelling argument, had he remembered to keep his l33t syndrome symptoms down. As it is, he sounds like a prat more than an intellectual.