"I'm stuffed" in the U.S. means "I've had too much to eat", but apparently in Australia it means you've had sex? I was told this by a friend who repeated the phrase in an Sydney restaurant and got funny looks, but it sounds far fetched to me.
As an Aussie I'm calling "rubbish" on this one. I've only ever used, and heard, "stuffed" to mean either really full or really tired.
In reference to fortnight - I had never realised that this was not a universally used term Fascinating!
I have noticed that people in the US will reference a time by the season, e.g. last summer, next winter. Now I'm not sure if it's a regional thing, but I tend to find that people here will tend to refer to the month, e.g. in July, last December. What do other countries do?