Kick the bucket
This is a light-hearted way of saying that someone has died. You certainly would never say to your neighbour: 'I am sorry to hear your husband has kicked the bucket.' You might use the phrase when talking about a bad film in which a character finally dies after several close shaves. 'Has he finally kicked the bucket? About time, too!'
Or you might use the idiom during conversation but you wouldn't want to get too serious. 'Well, we all kick the bucket some day, don't we?' or 'When I kick the bucket, I don't want people to make too much fuss'. It is far more acceptable to talk of our own death light-heartedly than that of others.
Where does this idiom come from? How can buckets and kicking them have anything to do with death? Some people rather desperately (but cleverly) try to connect them by referring to people who commit suicide by hanging themselves. You attach a rope to a beam, stand on a bucket, and kick it away with fatal results. It is unlikely, however, that this was common enough to give rise to the idiom. And why not use a stool or a chair?
The idiom actually originated from the way pigs were slaughtered in the past. They were hung upside down on a piece of wood called a bucket. Their heels kicked against it as they died, so to 'kick the bucket' was to meet your end. The phrase was gradually extended to humans and it is still used today.
Break a leg
It is a tradition (though it seems to be only about 100 years old) to wish an actor a broken leg as they prepare to appear on stage. This is an attempt to ward off evil forces by wishing one's fellow-performers the opposite of good luck. Some people have recently started using the phrase in other situations, like saying it to a basketball player before a match.
Saying the opposite of what you mean is not all that unusual. In some cultures, parents give their children unpleasant names to keep the dark forces away.
The origins of the idiom are unclear. Here are some possible explanations. We are told that in Shakespeare's time, break a leg meant to take a bow. But if the idiom wasn't used in the 17th century, how does that help? Why would an idiom suddenly appear out of a long forgotten phrase?
When John Wilkes Booth assassinated Abraham Lincoln in a theatre in 1865, he jumped on the stage and broke his leg as he attempted to flee the scene. Some say this gave rise to the phrase. Perhaps, but where is the luck and why did it take so long for the phrase to be used?
It also seems German pilots in the first world war used a phrase that translates as 'a broken neck and leg' before taking off, presumably to keep off evil spirits. This is said to have spread into the English-speaking theatre. Maybe.
Anyway, readers, break a leg!