The ornamental design for an insulating cupsleeve, as shown and described.
FIG. 1 is a top perspective view of an insulating cup sleeve showing the new design;
FIG. 2 is a bottom perspective view of the insulating cup sleeve shown in FIG. 1; and,
FIG. 3 is a front elevation view of the insulating cup sleeve shown in FIG. 1. The surface pattern continues all the way around onto the right, rear and left sides of the insulating cup sleeve.
The features shown in broken lines depict environmental subject matter only and form no part of the claimed design.