So maybe Hux keeps his neatly laced tall leather boots on during spars with Ren and a poorly blocked kick busts his nose and splatters blood onto Hux's polished boots.

Maybe Ren carries a wounded Hux out of harms way while he dribbles blood onto Ren's boots, after a couple whirlwind tours theough medbay to get bacta-patched back together Ren makes sure Hux learns the error in his ways.

Either way I would love some subserviance and maybe a little disgust and mos def some blood on black leather. Not really picky who's cleaning who's boots, doesn't have to lead to pure smut either.