when a person wears a jacket without the sleeves

[alpacinou]

How can I describe a situation when a person puts a jack on his/her shoulders without putting their hands into the sleeves?

This picture may help:

 

[emsr2d2]

He/She has put their coat round their shoulders. (BrE)

 

[Yankee]

Dumb.

 

[Amigos4]

How can I describe a situation when a person puts a jack on his/her shoulders without putting their hands into the sleeves?

The style you are referring to is called "draping". It dates back to aristocratic times, where the royals showed their elite status through extravagant clothing, and traditionally regal pieces like robes and capes were draped elegantly across one’s shoulders — a sign of wealth and influence. Today's fashion statement is the "Diva Drape" and is showcased by celebrities such as Melania Trump, Kim Kardashian West, Meghan Markle, and a bevy of other fashion divas.

 

[emsr2d2]

I'm sure Amigos is right about that in the circles that those people move in but we plebs (in the UK, at least) would just say what I said in post #2.

Mum: Put your coat on, Sam!
Sam: I don't want to. I'm hot.
Mum: Well, just put it round your shoulders then. I'm not carrying it anymore!

 

[Amigos4]

He/She has put their coat round their shoulders. (BrE)

He/She has put their coat around their shoulders. (AmE)