In SLabotka of old, the bochurim knew who and what they were. Today, if a bochur were to dress like a university student, he would think that he is one and therefore will act like one.
A purim story was told of a yiddishe shikkur (drunk) in the shtetel, that one time while he was in a drunken stupor, the shtetel children pulled a purim prank on him and dressed him in clothes of a priest . When this poor yid awoke, he passed a window and saw his reflection and started to believe that he is a priest….but yet he remained confused because in his heart he knew that he was a Jew,, but the eyes don’t lie and he sees himself dressed as a priest.
Toi solve the problem, be decided to test himself. Everyone knows that priests can read Latin. He will find a Latin book and if he can read it – that is a simon muvhak that he is a priest, but if he cannot read it, that proves that he isn’t a priest but a yid.
He found a Latin book and couldn’t read a word – what a simcha! Now he knew that he is a yid!
But then he got a rifyon (a machshava ra’ah) – maybe b’emes he really is a priest, and there might be some priest that can’t read Latim.
If bochurim today would dress like priests or university students or in goyish non-yeshivish clothes, they will think they are priests. To test if they are yidden or not, they will open a sefer – and lo and behold, they can’t understand the sefer. But know, that is no raya, because there are some bochurim that can’t understand seforim (and there are some priests that can).
L’chaim!