Or in its original form 'That's no ma wee dug (that shat
on yer lawn)'
It's a poster we had up in a tech support area of a software company I once worked in. The poster consisted of a picture of a small Terrier dog with a red line through it and the words 'That's no ma wee dug' printed in big red letters below.
We supplied the application software but for some reason the lusers would call us with regard to any problem relating in any way at all with their computers. Common complaints included the fact that they had generated a report and tried to print it but the printer had jammed.
At first we tried to explain patiently that this was nothing to do with our software and not something they should be phoning us about. Eventually, at around the time the company was in poor financial states and laying people off, we just said 'That's no ma wee dug' and put the phone down.
I've since used it in many a tech support situation, but these days I'm usually polite enough to explain what I mean.