Well, there are actual numbers you can assign to this, and they did that very thing in the UK. They assigned a "unit" as a standard measure of alcohol per drink, and have a recommended maximum and per-session amount of units. In the UK, 1 "unit" is one 330mL bottle with 2.9% of alcohol by volume. The maximum recommended is 28 units per week (for a man) and 21 units per week (for a woman), not to exceed 7 units in a sitting.
What does that translate to in US terms? Well, 1 unit in the US is defined as one 330mL bottle with 5.6% of alcohol by volume. By adjusting the numbers accordingly, this leaves about 16.5 drinks per week for a man, 12.4 drinks per week for a woman, not to exceed 4 drinks in a sitting.
That is, assuming a proper diet and hydration, no prior history of liver disease, no family history of liver disease, not taking acetaminophen or other drugs metabolized by the liver, etc.