Sorry, but the misunderstanding here is yours. Just war theory requires CBs to meet a specific set of criteria to be considered justified by the international community. There has never been a convention or remote consensus on Bob on what does and does not constitute a "just" CB. Likewise, just war theory does not validate or invalidate the CB itself; in that respect, it is logically agnostic to validity since justification =/= validation. Thus, without going into the minutia of copy and pasting definitions, a CB can be valid so long as it is logically consistent. Moreover, you presume that just war theory has a monopoly on military ethics; it does not. Concepts such as consequentialism, realism, militarism, and pacifism all use the identical concept of CBs with different perspectives on justification. Again, all of these theories are agnostic to the logical validity of the CB; they are only interested in the justification of the CB, which widely varies dependent on your school of thought. So while "I don't like you so I am going to kill you" may not be justified to you, it may be justified to others depending on their predilections. More importantly, however, is that regardless of your school of thought, the CB is valid because it is logically sound. It harkens back to the ancient concept of proschemata: fear, glory, and self-interest. There has been no convention or remote consensus on Bob delineating strict justifications of CBs either, so your argument is untenable to begin with.