To dream of a mustache represents not caring about what you are saying, or about the consequences of it. Often negative things you are saying to or about other people. A lack of concern for others feelings what what you are saying. Awareness of yourself or others speaking to others like a “total asshole.”
Example situations that may trigger a dream with a mustache in it may be name calling, rude remarks, or insensitively speaking of the dead when you someone is grieving.