common, ordinary, plain, familiar, popular, vulgar mean generally met with and not in any way special, strange, or unusual.

common implies usual everyday quality or frequency of occurrence

and may additionally suggest inferiority or coarseness.

ordinary stresses conformance in quality or kind with the regular order of things.

plain is likely to suggest homely simplicity.

familiar stresses the fact of being generally known and easily recognized.

popular applies to what is accepted by or prevalent among people in general sometimes in contrast to upper classes or special groups.

vulgar, otherwise similar to popular, is likely to carry derogatory connotations (as of inferiority or coarseness).

coarse, vulgar, gross, obscene, ribald mean offensive to good taste or morals.

coarse implies roughness, rudeness, or crudeness of spirit, behavior, or language.

vulgar often implies boorishness or ill-breeding.

gross implies extreme coarseness and insensitiveness.

obscene applies to anything strongly repulsive to the sense of decency and propriety especially in sexual matters.

ribald applies to what is amusingly or picturesquely vulgar or irreverent or mildly indecent.