A poet who has consumed a pharmacologically significant quantity of marijuana, or who makes a habit of doing so prior to writing.

Also, what you will appear to be on Usenet or a mailing list if your news or mail client generates articles with excessively long lines, as your readers' clients wrap your long lines down to their screen or window width. It is best for your client program to word wrap at 60 to 70 characters per line, so that even after several levels of  > > quoting  are introduced, your lines will stay on one line.

This rule stems from the days of eighty-column teletypes and, later terminals; for historical reasons, eighty columns remains a standard width for terminal windows, mail clients, and newsreaders. The ten to twenty spaces of slack allow for the various styles of quote indentation, as well as slightly narrowing the overwide text column.

Stoned poet Usenet posts tend to look something
like
this, but (naturally) with longer lines.  They
are
notoriously hard to read.

Did you know that studies indicate that narrower
columns
(around two to four inches) are easier to read 
than 
long horizontal lines anyway?
The stoned poet effect can be achieved in HTML with the overuse of the BR tag, or (as above) by using the PRE tag and manually mangling the line breaks.
The term "stoned poet" to refer to the victim of this word-wrap catastrophe appears to have originated with Thomas Mandel and Gerard van der Leun's book Rules of the Net, in which afflicted postings were compared to "the computer equivalent of bad blank verse by a stoned poet." Vigilant noders will note that this node does not plagiarize Mandel & van der Leun.