>>>>The above paragraph is a random pick from what I say to anyone saying that we geeks talk our tecnho jargon and introduce our own words into common language. Now it was OK for blacksmiths, horseriders, railroad guys and seamen to do that, and somehow only we get criticized when we do the same thing.
>>
>>>Aw, you're just blowing smoke. (where did that one originate?)
>>
>>Blacksmith to his apprentice? Pump it up...
>
>My guess would be a relationship to a magic show, where smoke is often used to deceive or help the deception.

Maybe - but the colloquialism was incomplete. There is supposed to more:
You're just blowing smoke up my ...

What else could be blown there? Before laxitives and [still] in cultures where laxitives are not available, parents sometimes do this to their children to relieve constipation (it's true) - not smoke - but air - a similar technique is employed to siphon gas from a car gas tank with a hose. The technique was to seal the gas tank fill spout around the hose with the hand - and blow. The additional pressure inside the tank would force the gas out. Now there is a technique whereby the siphonee sucks on the hose to start the flow. Risk - some may drain into mouth.

I hope this helps!