There's no doubt about it
A cup of tea
Used to reason, "lets be reasonable here". Said when someone is being unreasonable
Said to someone who is very very angry, usually on hearing this the person will get angrier
This adjective doesn't have a meaning, when you hear it being used just nod you're head in agreement.
Said when someone makes a blunder, at the same time you hit your forehead with an invisible ice-cream cone