Zest the lime with a fine grater or zester, avoiding the bitter white pith, and set aside.
Squeeze the juice from the lime directly into the blender, removing any seeds.
Add the frozen blueberries and honey (or syrup) to the blender.
Pour in ½ cup of cold water or ice, depending on how thick you want the slushie.
Secure the lid tightly and blend on high until the mixture is smooth, icy, and vibrant purple, about 30-60 seconds.
Stop the blender and check the consistency; if it's too thick, add a splash more water and blend briefly again.
Taste the slushie and add more lime juice or honey if desired, blending briefly to combine.
Pour the icy blueberry lime slushie into glasses and garnish with a small lime wedge or extra lime zest if desired.