I have a couple things.
Firstly, using prescription strength hydroquinone (Obagi) around my eye area. Ugh. If I could go back and slap myself silly for thinking this was a good idea, I would. It only helped to further thin the delicate skin in this area.
Not going to the dermatologist quick enough to prevent acne scarring. Don't ever wait, acne scars are all but impossible to get rid of.
Dying my hair black (as a natural blonde)...Black dye is damn near impossible to get out of your hair without making it feel like brittle straw. In the end, I had to cut all my hair off and start over. It was pretty traumatic.