The ornamental design for a beveragecontainerinsulator, as shown and described.
FIG. 1 is a frontal perspective view of a beverage container insulator in accordance with the present invention, wherein a portion shown in dotted lines being disclaimed from the design;
FIG. 2 is a frontal perspective view of the beverage container insulator of FIG. 1 in a partially flattened configuration;
FIG. 3 is a front view of the beverage container insulator as shown in FIG. 2;
FIG. 4 is a rear view of the beverage container insulator as shown in FIG. 2;
FIG. 5 is a left side view of the beverage container insulator, wherein a right side view is a mirror image of the left side view;
FIG. 6 is a top view of the beverage container insulator as shown in FIG. 2; and,
FIG. 7 is a bottom view of the beverage container holder as shown in FIG. 2.