The ornamental design for a thighexercisemachine, as shown and described.
FIG. 1 shows a perspective view of the present design.
FIG. 2 shows a front view of the present design.
FIG. 3 shows a rear view of the present design.
FIG. 4 shows a left side view of the present design.
FIG. 5 shows a right side view of the present design.
FIG. 6 shows a top view of the present design.
FIG. 7 shows a bottom view of the present design; and,
FIG. 8 is a top view of the design, shown in an alternate position.
The broken line showing of a thigh exercise machine is for the purpose of illustrating portions of the article which form no part of the claimed design.