Bicep... on a talking skeleton...[Mutters something along the lines of: "I'm pretty sure that's just your humerus you sack of bones." but then comes the theory about laundry.

He...never did his own laundry so who knew? That had always been Pennyworth's job so...could work?]

Can always try and see...or return those clothes to their owner and summon a similar pair from the closets in your size?