Hakuba had noticed, after some observation, Kuroba's unusually good personal grooming habits. At first – for a while, really – it had seemed to him that good grooming was the only good habit that Kuroba possessed. Indeed, after one particularly bad (and noticeable) pimple, he had even sought to emulate Kuroba's thoroughness.
Until he noticed, finally, that Kid never left even the slightest trace of himself at any of his heists. It wasn't only fingerprints that he neglected to leave behind (which really, any two-bit burglar knew not to leave), it was so much as a single hair, or a single piece of dead skin.
Kid left nothing, as if he were really a phantom. The reason then, for Kuroba's nearly obsessive attention to cleanliness became abundantly clear. It left a bitter taste in Hakuba's mouth. It also made him realize that Kuroba – Kid – was worlds better than he had ever given the thief credit for.
He realized then, that he had a long way to go before he could catch Kid. It only made him work harder.