The professional drinker regards his habit as an art form. All the little twists and turns of alcohol have burned their indelible /msg's into his remaining brain cells. He (or she) knows exactly what to expect from every drop of liquid drawn from the cup. The stages are enumerated in groups of tens.
This is why the Professional Drinker would never be caught dead in any situation where several amateurs are known to imbibe.
For instance, it is highly unlikely that you will see a Pro at any New Year's Eve festivities. This is the worst night of the year to try and snake your way through a plethora of wannabe drunks. Other events usually avoided: