Here is a fully compliant regex. It is nasty. http://ex-parrot.com/~pdw/Mail-RFC822-Address.html

caveat: It is the worst undeleted question in history through 2/7/13. It may be possible to browse here for a worse deleted question: http://data.stackexchange.com/ , but I'm not sure if they remain in the database.

It has gone through over a dozen revisions and isn't nearly as horrible as it once was. http://stackoverflow.com/posts/3455660/revisions

Note: The method that I used to locate this (stackoverflow) did not show the worst non-deleted question, but stopped at the second worst.

Using data.stackexchange.com, I located this: http://i.imgur.com/nmrP3Xe.png

Sorry for the misleading title, according to stackoverflow site search, it was the worst (questions => sort by vote => last page, last result)

The author of the answer has set multiple world records for calculating digits of pi. I highly recommend browsing through his answer history. You can learn more from his answers than from entire computer science classes.

http://stackoverflow.com/users/922184/mysticial

For those interested in a Stack-Ed perspective of Mysticial's l337ness (top 5 tags):

C++: http://www.stack-ed.com/#tag/c%2B%2B/user/922184/Mysticial

Performance: http://www.stack-ed.com/#tag/performance/user/922184/Mystici...

Language-Agnostic: http://www.stack-ed.com/#tag/language-agnostic/user/922184/M...

Optimization: http://www.stack-ed.com/#tag/optimization/user/922184/Mystic...

Branch-Prediction: http://www.stack-ed.com/#tag/branch-prediction/user/922184/M...

"The 1 and 2 character names are common because in earlier versions of Basic, variable names were restricted to 2 characters max."

Straight out of the stone ages