A Welsh joke now we're on nationalities
A man living in a North Wales village that was still operating the "no drink on Sunday" laws used to sneak out for a pint and a game of darts after mid-day lunch on Sundays to his local, where the guv'nor would serve his regulars illegally - this infuriated the drinker's religious wife no end, but she "nursed her anger to keep it warm" usually   
One Sunday afternoon, as he set off, she said ominously, "Don't you dare be late today - it's my mother's birthday and she's coming to dinner; you know she doesn't like you as it is - don't you dare stop late to play darts"
"I won't love" he said and set off, promising to return in good time
When he arrived at the pub he found it empty - all his mates, including the guv'nor had gone to the big match in Liverpool and the only person there was a rather attractive young woman who had agreed to mind the pub for the day and stop over till the landlord got back
He ordered a pint and asked the woman if she'd join him - which she did
They chatted for a while till one thing led to another and they slipped upstairs into bed and made passionate love until they both fell fast asleep
Panicking, he threw on his clothes, shouted goodbye and ran down stairs; as he ran through the bar he hastily grabbed a piece of chalk from the dart-board and shoved it behind his ear
When he arrived home he found his wife speechless with fury; "My mother arrived on time, waited and waited until it was obvious you weren't coming and left if a blazing temper swearing she never wanted to see us again and would leave her house to the cat's home - where the hell have you been till now?"
"Well love, to tell you the truth, when I got to the pub I found the lads had all gone to the match in Liverpool and the only one there was a temporary barmaid
We got chatting, bought each other drinks, and... well, you know - one thing led to another, we went to bed together, fell asleep and woke up about twenty minutes ago".
"You're a lying bastard" she spat, "You've been playing darts; you've still got the chalk behind your ear"
Jim