How can a sentence be a euphemism?

A sentence can be a euphemism if it expresses something that might be considered 'unpleasant' in a way that might be considered 'more pleasant'. Another way of describing this is to say that a euphemism is a way of avoiding telling the truth.

For example:

'My brother was very tired and emotional when he came home last night.' (This means that he was drunk.)

'Mary has a tendency to speak her mind.' (She is tactless.)

'Peter told me that his father had passed on.' (He had died.)