The ornamental design for a three-dimensional discard bag, as shown and described.
FIG. 1 is an isometric view of the three-dimensional discard bag showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a side view thereof;
FIG. 4 is a back view thereof; and,
FIG. 5 is a bottom view thereof.
The portions shown in grayscale patterns with a opacity and dashed lines within the design in FIGS. 1-7 are for illustrative purposes only and form no part of the claimed design.
The broken line showing of portions of the claimed design is included for the purpose of illustrating environmental structure and forms no part of the claimed design.