This Scottish dialect term is imitative, meaning it comes from the sound or usage of the word — in this case, it’s related to “whirl.” If you’ve ever seen a log rolling competition, making the spinning motion of the logs is specifically called “birling.” The other usage of this word in Scots slang applies to a raucous night of drinking. To birl is to drink with a crowd of people, and the phrase “birl the bawbee” means “to spend freely, especially for drink.” You want to invite the person who birls the bawbee out for a night at the pub.