An elongated bottle microresonator with parabolic nanoscale effective radius variation possesses series of dense and equally spaced optical eigenfrequencies. The separation of these frequencies can match the eigenfrequency of its axially symmetric acoustic mode. At very low temperatures corresponding to very high mechanical Q-factor of the resonator and low noise, the axial series of both optical and mechanical eigenfrequencies are well defined. Then, natural acoustic oscillation of the bottle resonator can parametrically excite optical modes and give rise to a highly equidistant and moderately broadband optical frequency comb. The teeth spacing of this comb is independent of the input laser power and the amplitude of mechanical vibrations. The acoustic mode required for the generation of this comb can be excited by the radiation pressure of an optical mode modulated with a natural mechanical frequency of the acoustic mode. Surprisingly, it is shown that in addition to acoustic bottle resonators (which are similar to optical bottle resonators) there exist antibottle resonators, which have the shape of a neck formed along the optical fiber, and, nevertheless, can fully confine acoustic modes.