Shamelessly copy-paste from my sister’s blog.
Waktu di acara bonenkai, gue, kakak, dan teman-teman melihat banyak yuurei berkeliaran alias orang-orang yang salah memakai yukata. Dalam memakai yukata ada aturan tersendiri, kalau salah malah ntar kita sama saja dengan yuurei alias roh. Yang gue sebal, pas gue kasih tahu ke panitia yang menyediakan jasa foto yukata, dia defensif mengatakan dirinya adalah dosen bahasa Jepang BHI. Gue mengajukan argumen-argumen yang ditanggapi setengah hati dengan ucapan “gomen nasai” sambil balik badan.
Jadi teman-teman, jika kalian hendak memakai yukata, pakailah dengan cara yang benar. Ini kutipan email kakak gue dengan temannya yang orang Jepang mengenai cara memakai yukata :

Sister: Which part of yukata should be in front of the body of the person who wear it? Is it Is it the right part or the left part?

Friend: Correctly, the left part (from the viewpoint of the person who wears it) should be outside (front), and the right part should be inside (back). In the viewpoint of other people in front of you, your kimono’s right part is in front of your body.

See this picture. This is the correct way.

This is the common way of wearing Japanese clothes, not only for Yukata, but
also for Kimono in general. There is no difference about this way between men
and women.

Confusingly, this correct way of wearing is called “Migi-Mae” (means
“Right-Front”) in Japanese, because your kimono’s right part is in front of your
body. [catatan: dari sudut pandang orang di depan si pemakai]

“Hidari-Mae” (means “Left-Front”) is the wrong way. Not only wrong, but also
ominous, because it is the way of wearing for the dead people in the coffin.

There are many people (especially young ones) who don’t know this correct way of
wearing here in Japan too.

In Japan, we often see old ladies seeing young girls wearing
Hidari-Mae/Left-Front kimono and crying “Oh, my god! Are you a dead person?”