I got this wonderful grey/brown sweater once that I loved. It was just big enough that I would describe it as "comfy". I decided to wear it to work one day and was immediately told I looked like Gimli in that LOTR scene where he tries to wear human sized armor... 😭
"Greyshirt" was a short lived comic hero. Based on 'The Spirit" the hero wore mundane clothes with a face mask and fought crime with his fists and wits. Grey shirt refers to the chainmail armor he wore underneath his dapper suit.