I have been reading Jeeves and Wooster recently, and the latter character says "don't you know" a hell of a lot. Eg. "He's my manservant, don't you know?" "Tea is very good after a journey, don't you know?"
I am interested in the origin of this phrase. I'm sure it is upper-class British but Googling this gives me no information.
Best Answer
'Don't you know?' or the variant 'don't you see?' dates at least from the late 19th Century--and it is irritating. My grandfather would make what he thought was a profound statement and then tack on the condescending 'don't you see?' as if his wisdom had fallen on the uncomprehending ears of an idiot.