Conveying emotions in writing is particularly tricky but also an essential skill if you want to write. The basic rule of thumb should be that you do not declare the emotion of an action or a line of dialogue, because doing it explicitly is not elegant, and the clear mark of the amateur.
“Two sugars and no milk,” she said angrily.
… in other words, is not the best we can do as we write a scene in which an afternoon tea turns into a duel with cake knives.
We need to find a way around it.
This is not, of course, an unbreakable commandment – but as usual when writing, we need to keep an eye out and try to suggest tone and mood tot he readers without telling them.
This is the notorious show-don’t-tell rule, that’s generally abused by first-timers.