"I'm stuffed " could only mean 'full, replete, had a sufficiency" at table in Britain. Otherwise it means "Now I'm in trouble", "I've got a big problem now". On the other hand 'Get stuffed!" is not an invitation to eat too much! It's said to men and women .It is not taken to mean "Go and get pregnant !" or "Go and have sex!" It means "Go away!" and may ,or may not, be meant as a hostile or angry 'request': it can be a robust , but friendly, expression of disbelief or of a wish to be left in peace. In these instances 'stuffed' is most likely a reference to taxidermy than to anything sexual.
'Knocked up' can mean pregnant here but 'to knock someone up' means to wake. We say e.g."Would you knock me up at seven" for Will you wake me at seven?". It's a reference to someone knocking on the door or window to wake someone. Years ago, in textile towns, the employers employed someone to go down the streets where the workers lived, knocking on doors and windows to wake the workers in time for the start of their shift at the textile mill. That person was called 'the knocker up'.
"Hello, I'm Randy" is may be the cause of a smile. Randy is not a common name in Britain. 'Randy' means 'sexually promiscuous' here ! And 'broads' for 'women' is not used. The Norfolk Broads are not women in a county of England, Norfolk, but a series of inland waterways and lakes (called 'Broads').So saying to an American man "Have you tried the Norfolk Broads? They are beautiful and free to visit and you'll have a great time" may be misunderstood !
And parking places by the side of main roads are called 'lay bys', which may puzzle Americans