Do we have a citation ethics in science?
Citations have only one practical purpose: indicating to your readers where they can find the published material on which you built the work that's described in your paper (methods you used, hypotheses that your work support or contradict, etc.). 

Everything else is just more noise in an already too noisy signal. 

Citations should not be used to show deference to senior researchers, to increase citation metrics of a person's supervisor, nor to "grease the palms" of reviewers or falsely infer relevance to a given journal. Please refrain from doing such things, they hurt science.