What you see: Light brown scars on the peel, in a pattern something like broken lace
What it is: Wind scar
Eat or toss? Eat! This is only a superficial issue

The story: 
Wind scar is a rather poetic name, isn’t it? And it happens just as you might imagine — when windy conditions in the grove cause leaves or twigs or even airborne grit to repeatedly brush up against the fruit's exterior. As long as the scars are healed and dry, there’s nothing wrong with your fruit. 

This grapefruit looks to have suffered a repeated sandpaper-like exposure to, say, a neighboring branch. Most often the initial abrasions happen when the fruit is just a few weeks old. Scar tissue forms, and then grows as the fruit grows. 

SOURCES: 

Dr. Stephen Futch, Extension Agent IV, Citrus. University of Florida, Citrus Research and Education Center. Institute of Food and Agricultural Sciences. Phone interview.

Photographic Guide to Citrus Fruit Scarring. University of California. Division of Agriculture and Natural Resources. 

Identification of Diseases, Peel Injuries, and Blemishes of Florida Fresh Citrus Fruit. Scientific Research Department. Florida Department of Citrus. 

The answer, my friend, is blowing in the wind...