an employee who mixes and serves alcoholic drinks at a bar- but most commonly used for males. In the US- barmen are called "bartenders".
In the UK- barmen are commonly Australian as they lack any social grace be employed where people may be offended by their constant pilfering and nasal whining accents. Australians are considered by British to have been specifically bred for the purpose of being barmen.
William: "Where's that new barman from?"
Harry: "Oh, he's an Aussie- they're bred for it?"
William: "What do you mean?"
Harry: "Aussies- they're only good for bar work."