What is it called when you have a skin condition that when you get bit by a bug and it leaves a scar no matter what you do?

It's called: It's called postinflammatory hyperpigmentation.

Unfortunate: There are many reasons for scar formation. You body's response to injury is the primary determinant of the appearance of the scar. With bug bites, other factors may come into play like: allergy, toxins or infection. For a specific diagnosis, you will need to see a doctor. A board certified dermatologist would be a good place to start.