To dream of a mug represents a situation you are experiencing where you refusing to embarrass yourself or get screwed over. Not allowing yourself to get "burned." It may also reflect your attempt to "put your foot down" or "draw a fine line" for someone who you think is going too far. Holding your ground.
Alternatively, a mug may reflect your refusal to embarrass yourself being too patient or trying something new.
Example: A man dreamed of a dark blue mug. In waking life he was giving a serious ultimatum to someone who had refused to pay him money that was owed.
Example 2: A woman dreamed of seeing her husband sitting at a table with a mug. In waking life she was seriously considering leaving her husband after he cheated on her.