The Free T-Shirt Day micro holiday provides permanent rewards. Better yet, since they take inventory space, you can destroy the item but access it at the transmog.

The Alliance Entertainer can be found in the Dwarven District. The mini-map will immediately trigger a ping sound and mark a star icon that you can also see in the Map. Instead of a vendor NPC, the Alliance Entertainer shoots T-shirts on the ground in random directions. You have to click the T-shirt to loot it.

The Horde Entertainer can be found patrolling the Valley of Honor, and briefly patrols into The Drag .

I am uncertain if more cities will get Free T-shirt vendors (considering this is still PTR), but so far there are none outside Stormwind and Orgrimmar, except for Shattrath City. You can find the T-Shirt Enthusiast vendor Selis Silksong in Lower City at TomTom coordinates:

/way Shattrath City:Outland 67.70 27.19

She sells Selis’ Silk Shirt.

These are the T-shirts given during the micro-holiday:

Randomly, you will be able to loot a “Free T-Shirt” item that lasts 1 day. When you click the item in your bag, it is consumed and makes invisible all your gear from the waist up except the T-shirt, and gives you a temporary title: “the T-Shirt Enthusiast.”

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