Just to play alittle armchair investigator...

A lot of unanswered questions. Seems like there is more to this story.

A lot of possible explanations, disagreement about who's gonna steer? Wrestling match ensues, boat veers into rocks?

Is there assumed liability in being either a declared or defacto designated driver? If so, that would seem to put a damper on anyone's enthusiasm to be one.

Good mystery movie story line there somewhere