The ornamental design for a cararmrestholster, as shown and described.
FIG. 1 is a perspective view of a car armrest holster showing my new design;
FIG. 2 is another perspective view thereof;
FIG. 3 is a perspective view thereof in a use state;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a right side view thereof;
FIG. 8 is a top plan view thereof; and,
FIG. 9 is a bottom plan view thereof.
The broken lines showing in FIGS. 1, 3, 4 and 8 depict portions of the car armrest holster and form no part of the claimed design. The broken lines shown in FIG. 3 further depict environment of the car armrest holster and form no part of the claimed design.