Wash and thoroughly dry strawberries. If they're not completely dry, the peanut butter won't stick to them.
Put peanut butter and coconut oil (if using) in a small microwave-proof bowl and place in the microwave for 20 seconds. Stir. You want peanut butter to be thin enough to be able to dip strawberries into it, but not super runny. If peanut butter is still too thick, place back in microwave for 5 second intervals, stirring in between.
Hold each strawberry by the stem and dip into the peanut butter, turning to coat all sides.
Sprinkle the sprinkles of your choice over the peanut butter and place strawberries on a parchment paper lined baking sheet. Put baking sheet in the fridge for about 20 minutes to let peanut butter harden.