You don’t say! is used to mean That’s obvious!
Children are not supposed to answer back.
Wishing well has to be read in context. A wishing well is a well-like structure, where people throw coins and make a wish. Well-wishers may gather outside a church before or after a wedding to show their support for the bride and groom. Wishing someone well is a kind of blessing or encouragement. I wish you well.
At a loss for words is a much nicer expression than gob-smacked.
Alphabetical order used to be the preserve of filing clerks and indexers. Now computers do it automatically!
Brainstorming is a way of generating ideas at random before assessing their value.
Lateral thinking is an older expression for thinking outside the box.
Read the riot act is a phrase with historic use. The Riot Act applied to gatherings of twelve or more people, who were expected to disperse after it had been read to them. Generations of disorderly children have been threatened with the Riot Act.
Give the low-down refers to the latest gossip.
Talk to the organ-grinder, not the monkey. An expression from long ago, referring to effective lines of communication.
Go to the top may mean speak to the manager.
I’ll wager… …to wager is to bet.
It’s bound to be… Bound means tied up. (It also means leap as in in leaps and bounds.)
I’ll be bound means I am fairly sure that…
I don’t want to deter you, but… precedes something which might!
I don’t want to detain you… …sometimes means I need to go now!
Waxing lyrical might need a little explanation. Waxing here has nothing to do with bees, candles or furniture polish. The moon waxes and wanes. Waxing means growing or becoming. Lyrical is to do with (flowery) words. Lyrics are the words of songs. So if someone is enthusiastic about something, they may wax lyrical.
A sharp tongue is one which habitually says unkind things.
A cutting remark hurts.
That would be tempting fate and Don’t tempt fate express the idea that it is not a good idea to say too much about the things hoped for in the future.
Don’t tempt me… is sometimes said to a child, who is deserving of punishment.
I tell a lie is often used in conversation, when someone realises they have made a mistake.
The book of the Bible which teaches about speech and the tongue is the Epistle of St James. James 3:1-12