Personally i say when the nipples point directly down.

Biomilq and the New Science of Artificial Breast Milk

Breastfeeding With Flat or Inverted Nipples

A surprisingly difficult question for Facebook: Do I have boobs now?, Technology

Why Are My Nipples Hard or Sore?

Are your nipples letting your breasts down? - ASAPS

nipple direction. an angle between a horizontal line passing through

Doctor-Approved Advice on How to Get Rid of Inverted Nipples

Normal Areola & Nipple Changes in Pregnancy

Downward turned man nipple? : r/nattyorjuice