This is a common misconception. While there of course are concerns for lifnei iver, placing a stumbling block (although I don't know if this would literally be transgressing the biblical prohibition, regardless the spirit of the prohibition is there), tsnius is something that applies at all times to all genders. This limited understanding restricts it to women in the presence of men, which is simply not true.
Take for example the second Simman of Shulchan Aruch Orach Chaim:
1 לא ילבש חלוקו מיושב (טור) אלא יקח חלוקו ויכניס בו (ראשו) וזרועותיו בעודנו שוכב ונמצא כשיקום שהוא מכוסה:
One should not put on his under-garment from a sitting position (Tur), but should rather take his under-garment and insert into it his (head and) arms while he is still lying down, with the result that when he gets up he is [already] covered.
אל יאמר הנני בחדרי חדרים מי רואני כי הקב"ה מלא כל הארץ כבודו:
One should not say (to oneself): "I am now in an inner room - who can see me?", for the Holy One Blessed Be He, "His glory fills the whole earth" (Isaiah 6:3).
Even in the privacy of one's own home, a person should be careful with how they appear. They used to sleep without clothes, so they shouldn't get dressed except under the covers. There's no specification of a man, or a woman, and mentions that no one else is around.
The Mishnah Berurah § 1 speaks this out explicitly.
דאז בהכרח יתגלה גופו והאדם צריך להתנהג בצניעות ובושה לפני הקב"ה ואפילו כשהוא לילה ובחדרי חדרים הלא מלא כל הארץ כבודו וכחשיכה וכאורה לפניו יתברך. וכן צריך ליזהר תמיד מחמת טעם זה שלא במקום הכרח מלגלות מבשרו ואפילו מעט כל מה שדרכו להיות מכוסה בבגדים לעולם
[Putting on clothes while sitting] will make it so that they have to appear uncovered, and a person should always act with tsnius and bashfulness in front of G-d. Even at night, even by themselves, since the whole world is filled with His glory, and night is like day before Him. For this reason, a person should always be careful not to reveal, without justification, even a little bit, any part of their body which is normally covered with clothes
Now, context is everything. What a person wears (or doesn't wear) in the shower is different than what they would wear in public. The level of tsnius a person has in their home isn't the exact same as in public, or the same as when they're in front of a prominent person. Whatever is normal is the rule of thumb, but the exact details aren't for this question.
The Semak (Sefer Mitzvos Katan) § 57, brought by the Biur Halacha § 3 s.v. יהא צנוע, understands tsnius to be the mitzvah of והיה מחניך קדוש, your camp should be holy (Deuteronomy 23:15). It's a mitzvah in its own right, and not simply subsumed in not causing others to stumble.