From the author's README on Thunderstore

Grateful_Dead_purple_tye_dye_long_sleeve

calm shirt if you like the dead

In game

In shirts section

Credits

Made by TerrapinRock

Install Grateful Dead purple longsleeve tye dye

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for Grateful Dead purple longsleeve tye dye and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.