the done thing 

Whatever practice society considers normal. It's something that a lot of people do only because everyone else does it (even though they don't realise it).

Women in the 19th century had hairy legs—not because they didn't have razors, but because it was the done thing.

Women in the 2000s have shaven legs—not because it looks or feels better, but because it is the done thing.

Women in the 2000s wear thongs—not because they are sexy, but because it is the done thing. If it was actually worn because it's sexy, it would have been done back in 1979.

the done thing by Michael March 19, 2004