A person who uses online messenger services to harass other people using the service.
These people then blatantly ignore the people they have harassed the next day in person, pretending it didn't happen.
Person1: "Dave gave me some jip last night on MSN, but today he was sound with me and pretended nothing happened."
Person2: "What a keyboard gangster"
Their are two definitions to this phrase.
1. A person who attempts to act badass behind their computer screens through their own keyboards. This definition is most commonly used by the populice that was tormented in upper-grade schooling and have no spine to speak of.
2. A person who throughly thrashes definition #1 using intelligence and wit only. This populice most commonly keeps to themselves until some fool comes along that needs to be slapped down properly, they do not go around looking to be badass, they just happen to have it come to them.
Def#1: blahblahyour an idiot i am great.
Def#2: instead of trying to be a keyboard gangster why not simply learn the definitions of the words you intend to use in everyday life, please vacate the premises before i make you feel as dumb as you look right now.