The ornamental design for men's underwear and swimsuit, as shown and described.
FIG. 1 is a perspective view taken from the front, right side of a men's underwear and swimsuit in accordance with the present invention;
FIG. 2 is a front elevational view taken of the men's underwear and swimsuit in accordance with the present invention;
FIG. 3 is a back elevational view of the men's underwear and swimsuit in accordance with the present invention; and,
FIG. 4 is a side elevational view of the men's underwear and swimsuit in accordance with the present invention with the left side being a mirror image.