Run a warm bath, and to it add a cupful of cider vinegar, a tsp or so almond oil and 15 drops lavender oil. Swish it around and get in. The aarghh will soon turn to aaahh!!
The cider vinegar takes out the sting, the oil replenishes the moisture and the lavender repairs the damage. This mixture will even help the red to go brown and not peel. For bad sunburn, apply lavender in rosehip oil after the bath to aid skin repair.