From the size of common beer containers (bottles and cans) in the United States: 12 ounces + curls, a weightlifting exercise. The notion is of lifting a can of beer to one's lips repeatedly.
12-ounce curls pl (plural only)
- (idiomatic) Drinking beer.
2006 June, Scott Quill, “Muscle Bulletin: Pass the Bar”, in Men's Health, ISSN 1054-4836:
- Don't burn out your biceps with 12-ounce curls.