SunnyD isn't citrus. It has less than 2% juice in it. It is junk food. While citrus is often on the list of no nos for chickens..I have seen many people say they give it to them now and then without issues..but you aren't giving them citrus, you are giving them sugar water with a bunch of chemicals and artificial dyes.. While I don't think a little bit now and then is going to kill them..it isn't anything that's really nutritional.
Sunny Delight Fact Sheet
Ingredients: Water, High Fructose, Corn Syrup and 2% or Less of Each of the Following: Concentrated Juices (Orange, Tangerine, Apple, Lime, Grapefruit). Citric Acid, Ascorbic Acid (Vitamin C), Beta-Carotene, Thiamin Hydrochloride (Vitamin B1), Natural Flavors, Food Starch-Modified, Canola Oil, Cellulose Gum, Xanthan Gum, Sodium Hexametaphosphate, Sodium Benzoate To Protect Flavor, Yellow #5, Yellow #6