1 Because he can.
2 To normalise prosthetics in full view.
3 To annoy ToraToraTora.
4 To distract attention from his vanishing hair.
5 To annoy ToraToraTora.
bednobs has it. Also, some double amputees find it difficult to put trousers on after they have put their prosthetics on, don't know if Billy struggles with it but I suspect he does because one leg was amputated well above the knee.
Thankfully, he can wear what he kin well likes.
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