jargon.artrocity.com
New Hacker's Dictionary the Jargon File v 4.4.6
[IRC; common] Under most IRC, /me is the “pose” command; if you are logged on as Foonly and type “/me laughs”, others watching the channel will see “* Joe Foonly laughs”. This usage has been carried over to mail and news, where the reader is expected to perform the same expansion in his or her head.