To start, prep your milkshake glass or vessel. Pick something tall and slender and chill it in the freezer for 10 minutes before you start. This will keep the shake cool and the frosting from melting.
Spread a nice, thick layer of frosting around the rim of your glass, going down 2-3 inches (5-7 cm). Now, this is where the fun starts: Stick your favorite candies and treats all around the frosted rim—candy, doughnuts, cookies, sprinkles...anything goes. Freeze for 10 minutes.
Now, make the milkshake. Combine the strawberry ice cream, vanilla ice cream, strawberries, marshmallow fluff, milk, and vanilla in a blender and blend until smooth and creamy.
Pour the shake into the decorated glass, top it with a hefty dose of whipped cream, and add whatever else you got! Animal crackers? Fetch, yes! Cotton candy? Bring it! A lollipop the size of your face? Why not?! A slice of cake made with rainbows and smiles? DO IT… We dare you.