Pasithea, are you seriously "upset" by a momentary glimpse of breastfeeding? Even if all you see is the baby's head and a small part of the mother's breast? How does that upset feeling manifest itself? Do you feel so distressed that you day is ruined, or do you simply feel mild disapproval? If the latter, you aren't actually upset; if the former, you've got problems that go way beyond this simple issue. And if it is anything in between, then you need to live with it.
Why do people think they have some sort of right never to be upset? I got upset when I just missed a bus today. Should I be entitled to demand that the bus company have buses on standby at every bus stop just to avoid me getting upset?