Pinkie Pie and Rainbow Dash are from Hasbro's My Little Pony: Friendship is Magic and this screenshot's taken from Valve's Garry's Mod.

Pinkie manage to create a balloon with unlimited air in it and tested it out on Rainbow Dash to help her fly easily, but only for her to instantly inflate and flew out of control, deflating with a farting sound out of her mouth. Looks like Pinkie made one kooky mistake here.