If I have a cold, how bad is it to have an alcoholic drink or two?

If one or two. Doesn't really make much difference. My experience is that when people are talking about "one or two" they are often really talking about ten or twelve. Alcohol in excess impairs our immune system, makes us more susceptible to infection, and those illnesses may last longer. If really one or two, it will not make any measurable difference in recovery. However, smoking will, and if you smoke, stop.
Alcohol and cold. Alcoholic drink will not cause any harm as long as you are not taking any strong cough medicine or antibiotics for the cold.One or two drinks will not harm if you are on no other medicine.