לזכות כ"ק מרן אד"ש שעומד לתרץ קושיא זו בשיעור ביום שני בעז"ה
The gemara [Bava Metzia 46a - see there] understands the Mishna to be discussing this seemingly odd case of a person who is standing naked on the threshing floor and thus can't perfom a kinyan chalifin. The gemara asks - ואיכפל תנא לאשמעינן גברא ערטילאי דלית ליה כלום? - Did the Mishna trouble itself to tell us such a remote case of a person who is standing naked on the threshing floor?
Why wasn't the gemara bothered by a different issue - to redeem Maaser Sheni [which is what the Mishna is discussing] one needs to make a bracha. How does one make a bracha while wearing what [unfortunately] many women in New York city "wear" in the summer?? [I like to be melamed zchus and call it "insomnia". They just forgot to get dressed.]
In the works of the Heilige Chebiner Rov ztz"l:
By the way - I hope the first law that our new president passes in office is that women must wear sleeves in public. We are a wealthy country and there is no reason that women can't add a little material to their wardrobe so that they become more human. Humans cover themselves. Non-humans don't wear clothing. It would be a nice gesture to all of the Jews who voted for him and a credit to America which will become a country that prides itself on tzniyus!!