Common White Shirt

Common White Shirt is a shirt item that can be purchased for from the following vendors:
 * in Loch Modan
 * in Stormwind City
 * in Darkshore
 * in the Exodar
 * in Ironforge
 * in Silvermoon City
 * in Silverpine Forest
 * in Northern Barrens
 * in Thunder Bluff
 * in the Undercity
 * in Orgrimmar
 * in Silvermoon City
 * in the Trial of Style Assembly Chamber

It can also be obtained from Free T-Shirts in Orgrimmar or Stormwind during Free T-Shirt Day.