Coarse, vulgar, gross, obscene, ribald are comparable when applied to persons, their language, or behavior and mean offensive to a person of good taste or moral principles.
Coarse is opposed to fine not only with reference to material things (as fiber, texture, or structure) but also with reference to quality of mind, spirit, manners, or words; it implies roughness, rudeness, crudeness, or insensitivity.
Vulgar (see COMMON 3) suggests something that is offensive to good taste or decency, frequently with the added implication of boorishness or ill breeding.
Gross (see FLAGRANT) is opposed to fine in the sense of delicate, subtle, ethereal; it implies either a material, as contrasted to a spiritual, quality or a bestiality unworthy of man.
Obscene stresses more strongly the idea of loathsome indecency or utter obnoxiousness.
Ribald suggests vulgarity and often such impropriety or indecency as provokes the laughter of people who are not too fastidious.