Isn't there an old saw about "trapping more flies with honey than with vinegar"? In short, as dustybin mentions, most crew respond well to a polite and genuine request for assistance, whereas the reverse will achieve the reverse. Human nature determines that you will resolve the issue of the person who is pleasant with greater enthusiasm than will be shown to the unpleasant person.
Fortunately, the overwhelming majority of people are pleasant, or are at least unintentionally not so. The hard-core of those who behaviour is unacceptable, and who know it to be so, remains very small.
My personal bugbear? (I probably shouldn't say this...) When boarding and disembarking I stand at the door, make eye contact with each person, smile and Greet them appropriately: It always seems to me that a normal human response would be to acknowledge that greeting in some way. Completely ignoring me always strikes me as requiring an effort of will, greater than that required to acknowledge me. It is surprisingly common for people to blank me out, and in my experience, it tends to be a British thing, and more common amongst those with the background and education to know better.