The ornamental design for a swimsuitbottom, as shown and described.
FIG. 1 is a perspective view of a swimsuit bottom;
FIG. 2 is a front view;
FIG. 3 is a back view;
FIG. 4 is a left side view;
FIG. 5 is a right side view;
FIG. 6 is a top view; and,
FIG. 7 is a bottom view.
The dashed lines depict portions of the swimsuit bottom that form no part of the claimed design. The dash dot dot lines depict stitching of the swimsuit bottom that forms no part of the claimed design.