Might actually have some merit.

Is that where the term comes from? I've often wondered.

Well thats just mental.

Hahah ending was awesome.

Ok, so it may have seemed to work once and people would continue to do it, but how in the hell did someone conceive of the idea in the first place?
Were they smoking something?

I love Stephen Fry. I love QI.

However, you've hit upon why I refuse to upvote this video. Not one mention of the idiom? Absurd.

My cursory research turns up that this belief/contraption is not actually related to the idiom "to blow smoke up one's ass". That saying is dated to the mid-20th century, when the rectal intensifier was added to the less crass "to blow smoke", which phrase derived from illusionist's use of smoke to distract the audience & disguise their surreptitious actions.>> ^kymbos:

Is that where the term comes from? I've often wondered.

Yeah, I did a little google search too. None of the definitions do justice to how I understand the phrase, which is to toady up to someone with undue praise.

A: You really are the only musician here with any real genius.
B: Stop blowing smoke up my arse.

The mystery continues...

Yeah, they still didn't quite make the connection between blowing smoke up one's ass and flattery. Maybe it was meant along the lines of "what you're doing is useless and irritating, please stop". And somehow it came to be used exclusively as a rebuke of flattery.

I see flattery as very closely related to "blowing smoke" (i.e. disguising one's true intentions). <shrug>

100th upvote!

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The duration of this video has been updated from unknown to 4:27 - length declared by radx.