The ornamental design for a key chaincharm, as shown and described.
FIG. 1 is a front elevational view of a key chain charm showing my new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a front and bottom perspective view thereof; and,
FIG. 4 is a bottom plan view thereof.
The broken lines showing various aspects of the lamp structure in FIGS. 1-4 are for illustrative purposes only to show the placement of the claimed design and form no part of the claimed design.