This is an old mod, but popular. It plays a Leeroy Jenkins sound clip.
Commands up to date:
I'm sure any of you who read the official WoW message boards (especially the off-topic board) know who Leeroy Jenkins is. If you don't go to the WoW off topic boards.
Then check out this movie: Worldofwarcraft.filefront.com
Anyway, this add-on adds a /leeroy command. When used, you yell "Leeeeerooy JEEENKIIIINS" and it plays the sound from the movie :)
Now also includes /leeroy chicken. That says 'least i got chicken' and plays the sound from the movie of course :)
Well, it came sooner than I expected. Now, others with the add-on near you will hear the audio too :) Many thanks to Humera from Shattered Hand who was really the one who added this in :)
You can now also type /leeroy author to see the credits (only me and humera so far)
Some of you may hear something other than what I hear. To change text, open up leeroy.lua and do a find on the word chicken. It will come (after a few clicks) to the string that you say. Simply change that string :)