The one that got me when I first moved here was "will you be eatin' in, or takin' away?" as opposed to the US usual "for here or to go"?
They talk so fast, I couldn't understand for the life of me what they were saying. I must have said "pardon?" five times. My kids tease me about it now.
Also, at Ikea, I was looking around for a cart. They all looked blankly at me until I played charades, then they showed me where the trollies were.