The ornamental design for a disposable lighter, as shown and described.
FIG. 1 is a perspective view showing my new design.
FIG. 2 is a front view thereof.
FIG. 3 is a rear view thereof.
FIG. 4 is a right end view thereof.
FIG. 5 is a left end view thereof.
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines immediately adjacent the shaded areas represent the bounds of the claim and all other broken lines are for illustrative purposes only. None of the broken lines form a part of the claimed design.