I know of a situation where before a wedding, the chosson’s brother was carrying the ring, and walking around the hall, and wandered into the room where the kalla was doing pictures.
So he held out the ring to the kalla and jokingly asked, “do you want this?” She said yes, so he gave it to her.
The Rav was in the room, and paskened it was kiddushin, since he gave her a wedding ring, and she was wearing a wedding dress, in a wedding hall. So she needed a get.
The problem was that even he gives a get, she will be an issur eishes ach to her chosson.
So the chosson killed his brother and did yibum.
It was in the NY times: http://tinyurl.com/43lq3pc