"You don't like doing anything for anybody except Mukuro-sama." Under most circumstances, this would seem like nothing more than a simple statement of fact, and not even an entirely accurate one. Chikusa doesn't like doing things for anyone, not even Mukuro-sama. It's more that he's willing to do things he doesn't like for Mukuro-sama, because he judges Mukuro-sama to be worth it. It's that his pleasure at helping Mukuro-sama outweighs the displeasure of making an effort for him.

Ken's been given the impression that Chikusa only humors him because it would be a bigger pain not to, as opposed to Chikusa actually enjoying doing anything with him or caring about him enough to do anything for him. Coming in second behind Mukuro-sama would be understandable, the way things should be between them; coming in last place, no higher than everyone else in the world Chikusa humors simply to avoid trouble with, stings.