Is it considered "marit ayin" if boys and girls stroll together on Shabbat?

Question

I have heard of a number of yeshivot that have a strict rule regarding boys and girls being with each other. Their rule is "simple" - outside of your own family members, it should be never for any reason.

Let's say Reuven's friend, Benzi (who are in the same class) has a sister, Talia. The three of them walk together on the street on Shabbat to visit their friends, Habakuk & Reut. Is this activity "marit ayin"? Keep in mind, that there is no prohibition, per se, even according to the yeshiva's rules about Benzi talking to Talia, as they are siblings. But, people don't know Talia, who don't know the family. Also, it IS against the yeshiva rules for Reuven to be with Talia.

Answer 1

Yes, it's Maaras Ayin Brachos 43b

ואל יספר עם אשה בשוק אמר רב חסדא ואפילו היא אשתו תניא נמי הכא אפילו היא אשתו ואפילו היא בתו ואפילו היא אחותו לפי שאין הכל בקיאין בקרובותיו

And one shouldn't talk to strangers in the marketplace.

Rav Chisda said that the law applies even with his wife, and a Braisa said that [this law applies] even with his wife, daughter or sister since not everyone is fluent in his relatives.

Answer 2

No. It is not Maaras Ayin.

The Gemara in Brachos writes:

ששה דברים גנאי לו לתלמיד חכם אל יצא כשהוא מבושם לשוק ואל יצא יחידי בלילה ואל יצא במנעלים המטולאים ואל יספר עם אשה בשוק ואל יסב בחבורה של עמי הארץ ואל יכנס באחרונה לבית המדרש

Six things are a disgrace for a Scholar: (i) he should not go out perfumed to the marketplace; (ii) he should not go out alone at night; (iii) he should not go with patched shoes; (iv) he should not speak with a woman in the marketplace; (v) he shouldn't recline in a group of ami haaretz; (vi) he should not go in last to the Bais Medrash.

The Gemara goes on to explain that this applies even if the woman is his wife, daughter or sister, but none of things listed here are issurim. They are actions that a Talmid Chochom should refrain from. They are beneath his station.

The Rambam similarly lists these halachos as things that Talmid Chochom should not do in Hilchos Deios 5:7. He does not list them with halachos that apply to all Jews or laws pertaining to interactions between men and women generally.

However, this does not mean that it is permitted for boys and girls--who are not siblings--to go for strolls together. It arguably prohibited, just not because of maaras ayin. Rather, the Shulchan Aruch writes (Even HaEzer 20:1):

צריך אדם להתרחק מהנשים מאד מאד ... ואסור לשחוק עמה להקל ראשו כנגדה

A man must distance himself from women very much ... and it is forbidden to laugh with her or to be lighthearted in front of her.

Similarly, it is prohibited to ask a woman how she is doing. Shulchan Aruch Even HaEzer 20:6

While the exact parameters of what it means to "laugh or be lighthearted" are not clear, I think a Shabbos stroll where they are just walking around and schmoozing is borderline at best. Flirting is definitely prohibited.