The beer effect occurs when you are in a restaurant with someone you don't know that well, and everybody gets like water or diet coke, until you order a beer, and everybody changes their mind and gets beer too :-)
Paul: - "I'll have a diet coke."
Sarah: - "I'll have a glass of water."
Martin: "I'll have a beer."
Paul: - "You know what, i'll have beer too. I don't want the coke.
Sarah: - "I'll have a beer as well"
Martin: "Yeah. Thats the beer effect."