Beat the room temperature butter & shortening together on medium-high speed for about two minutes, until all the lumps are gone.
Add in the powdered sugar & cover with a kitchen towel before turning on and mixing to prevent a mess.
Mix in the vanilla extract and two tablespoons of pineapple juice. If the frosting is too thick or not pineapple-y enough, add in up to two more tablespoons of pineapple juice.
Place into an icing bag with desired decorating tip.