I'm also mystified. The closest thing I can think of is when a newly-married couple are holding a glass of champagne each, and they link their drinking arms and then drink that way. Like this: http://farm1.staticflickr.com/72/165225556_51902237a5_z.jpg?zz=1 We don't really have a common phrase for it.

'locked' is also used instead of linked.."They locked arms and drank together."

There isn't a specific term for this custom in English so you have to describe it instead, like "drinking with linked arms." For example, you could say: They drank with linked arms.

I've never heard it