My clients and I have been testing there theory. So far Brown colored liquor seems to be an offender while clear doesn't seem to have much of an affect. We have tested for a year. Beer and wine were not in our study so I cannot comment.
Physiologically, the sugar just spikes that glycemic load resulting in immediate secretion of cortisol, which kicks androgen production into gear. Elevated testosterone and other androgenic compounds thicken sebum and irritate the pore lining, making it easier to rupture. Make it a habit, and the sugar may also feed bad microorganisms. The effect is not so bad with the person who sips one drink over the course of dinner, but the way a lot of people drink (empty stomach, goal of getting wasted, frequent and repetitive binges), they can really throw a wrench in their acne clearing process. Not only do the resulting hormones me it easier for acne lesions to form and easier for small impactions to undergo the inflammatory processes to become highly aggravated pustules, the overall inflammation load makes healing really really difficult.