The private parts of a man are between his knees and his belly. The private parts of a woman are her complete body except her hands, feet and face. She also cannot look at any other woman’s area between the knees and the belly; neither can show hers to any. One should never show his/her private parts to strangers.
Bahz ibn Hakeem narrated from his grandfather:
“O Messenger of Allah! Against whom shall we cover our private parts? I asked. He said ‘Cover your private parts against everyone except your wife and your handmaiden!’
What is the ruling if people are sitting altogether? ‘Try not to show your private parts to anybody!’
And then I asked what should someone do when he’s alone, ‘Whom, you need to be mostly ashamed of is Allah’ he said.” (Tirmidhi, Adab, 39; İbn Majah, Nikah, 27.)
However, looking at someone’s private parts or showing yours to someone else are not one of the things that break the fast.