This isn't mine, but it's still one of my favorite misconceptions.
It was sophomore year of college, and I was talking to my roommate, and he brought up how awesome it would be to have a bar with a tap at your house. The conversation pretty much went as follows.
Me: Well, I mean, we've had kegs here. It's pretty much the same concept.
Him: Yeah, but it's not like a bar. Kegs can run out.
Me: Yeah, but so can bars...
Him: Dude, I'm talking about having the same setup they have at bars.
I just sort of looked at him for a minute, confused.
Me: ... How do you think bars get their beer?
Him: ...
Me: ... Dude.
Him: You know... From the factory.
My mouth was agape. I was floored.
Me: Wait a fucking minute. Are you envisioning a complex network of pipes leading from breweries to bars around the nation?
Him: Yeah, exactly!
Me: Are you out of your fucking mind? :lol
Just to recap, my roommate that that bars were all connected to tubes that stretched out for hundreds of miles from "beer factories" to their taps.