Drinking alcohol until one reaches a state of utter bandiness where one cannot usefully function in any way in the physical world.
Often accompanied by bandy dancing where the limbs flail about in an uncoordinated fashion and usually results in excessive use of "pirate talk"

Not to be mixed with bandy candy

To drink alcohol in excess. Drinking so much your body and/or mind can't function right and you become 'bandy'. Occurrs in a group of friends who want to get as drunk as possible.