To get together with someone and sit somewhere and drink something. Can be coffee in a cafe or can be beer in a pub or just sitting in the park drinking a beverage. Depends on what the people getting together feel like. Generally means getting together to do nothing but have a conversation.
RJ hosts a morning live program called "Having a Coffee with RJ." Though the show is called "Coffee with RJ," everyone jokingly knows it as a pseudonym for "Masturbation."
