The ornamental design for a cuppaintgun, as shown and described.
FIG. 1 is a perspective view of a cup paint gun of the present invention.
FIG. 2 is a left side view of the cup paint gun.
FIG. 3 is a right side view of the cup paint gun.
FIG. 4 is a front view of the cup paint gun.
FIG. 5 is a rear view of the cup paint gun.
FIG. 6 is a top view of a cup paint gun; and,
FIG. 7 is a bottom view of a cup paint gun.
The broken line showing of the power cord is included for the purpose of illustrating portions of the paint gun and forms no part of the claimed design.