A place I worked at a while back
A marketing manager came to me to ask if I could give him an image I did at a higher resolution, so he could give it to another artist who did print work.
I said, How big do you want it. He said 300 dpi. I say, okay, but what sized image do you want? He said 300 dpi. I say, well how big are you going to print it. He says 300 dpi. I say are you going to print it on a full cover, or do you just need maybe only a quarter page
300 dpi, 300dpi, 300 dpi.
I eventually got him to say he wanted it printed 5x7 inches. I went ahead and made it larger just to be sure, but the sad part of the story is
I didnt know it but he was furious at me for weeks and ragged me big-time to my boss. Why? Because, he made a print of it, which happened to be exactly 5x7, because I thought to change the settings in Photoshop just incase he did print it. However, all of the images he had ever printed before happened to come out larger, so he thought I didnt give him a 300 dpi image.
I tried for months to get him and a couple of others to understand that dpi means nothing without image size, I even wrote up a little document with pictures and everything, and they never read it.
P.S. Another day, he told me he didnt need me to blow up video frames for him anymore. He would play them in Media Player at full screen, hit <print screen> and paste it into paint. 
Ohmanoggin