You do a check around the store to see if everyone else has gained a boner, because of the body you developed, which was something you needed to figure out based on everyone laying down with smiles on their faces as you walked passed them. You of course suspected that it wasn't just happening with men either.
As you walked passed the women in the store, you saw that they were sprouting penis's whenever they saw your feminine body, which means that the store you were in was starting to make you uncomfortable. You take the milk that the cashier bagged up for you once you've paid for it, and then leave the store, but suddenly what happened in the supermarket was the start of your problem. People kept getting boners even after you left the supermarket which was making you more uncomfortable.