I was in Woolworths around Christmas time and asked the till girl for 24 first class stamps. She told me that they "didn't do 24 first class stamps" so I asked if they had them in 12's or 6's , to which she said "yes, but you want 24, don't you?"
or
On holiday in France last year, after we'd all been out for a meal, the local gendarme pulled in my brother in law for a spot check. after pulling up behind him, and getting out to help (i was the only one who could speak a bit of french), i heard his wife say to the gendarme "pardon monsier, mais parlez-vous francais?"
The look on the copper's face was priceless.