When I was in my early 20s, an wise old man (probably 40) told me that anytime he is drinking with people, especially competitors, he takes the bartender aside and tells him each time that he orders a gin and tonic, hold the gin. Put the tonic in the same sized glass, and charge him for the drink.
That way, everyone around him got drunk while he stayed sober.
He learned a lot that way.
Over the years, so have I.