The ornamental design for a beveragecontainerinsulator, as shown and described.
FIG. 1 is a first perspective view of the beverage container insulator;
FIG. 2 is a right-side view of the beverage container insulator;
FIG. 3 is a front view of the beverage container insulator;
FIG. 4 is a rear view of the beverage container insulator;
FIG. 5 is a left-side view of the beverage container insulator;
FIG. 6 is a top view of the beverage container insulator;
FIG. 7 is a bottom view of the beverage container insulator; and,
FIG. 8 is a second perspective view of the beverage container insulator.
The broken lines in the drawings illustrate portions of a beverage container and a decorative pattern on the exterior of the beverage container insulator which form no part of the currently-claimed design.