The ornamental design for a flip flop shotglass, as shown and described.
FIG. 1 is a front view of a flip flop shotglass, showing my new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a top perspective view thereof;
FIG. 4 is a top view thereof; and,
FIG. 5 is a bottom view thereof.
The broken lines showing portion(s) of the flip flop shotglass are for the purpose of illustrating environmental structure only and forms no part of the claimed design.