Every installation I am aware of has an alcohol policy. Some address the issue of consumption in uniform and others do not. For Example: Ft Carson CG Policy 03 covers alcohol. It does not address drinking in uniform, but does address no alcohol consumption during duty hours by Soldiers on duty. It further states that the duty day is not standard times but as established by the unit and/or duties being performed by the Soldier. This means a Soldier performing 24 hour CQ is on duty for the entire 24 hours and cannot go have a beer with dinner.
It also covers no alcohol during deployment or training, including if during training you return to your residence during off duty hours, you are still considered as being deployed and/or in training and consumption of alcohol is prohibited.
I do know that General Order #1 in Iraq and Afghanistan prohibits the consumption and possession of alcohol at all times.
Without a specific post/unit signed policy letter against drinking in uniform, AR 670-1 does not prohibit drinking alcohol while in uniform. Should there be a policy letter prohibiting it, a violation would be covered under Article 92, Disobeying an Order or Regulation, not Article 134.
AR 670-1, Paragraph 3–3. Occasions for wear
a. Soldiers may wear BDUs on duty when prescribed by the commander. Soldiers may wear BDUs off post unless prohibited by the commander. They may not wear BDUs for commercial travel, unless authorized by para 1–10c of this regulation. Personnel may not wear BDUs in establishments that primarily sell alcohol. If the establishment sells alcohol and food, soldiers may not wear utility uniforms if their activities in the establishment center on drinking alcohol only.
b. Utility uniforms are not normally considered appropriate for social or official functions off of the installation, such as memorial services and funerals. These uniforms are issued as organizational utility, field, training, or combat uniforms, and they are not intended for wear as all-purpose uniforms when other uniforms are more appropriate.