Madonna
(adj.) A person who refuses to use their last name in signature file, voicemail, email address or website. In doing so, claims 1st name status like the singer Madonna, and also suffers from Madonna-ish complex that he/she is so important, they do not need to use a last name because everyone should just know who they are; Creates confusion and frustration in corporate environments.
Used in venting frustration, such as: 

Why does this guy Aaron keep leaving me voicemails & sending emails with no signature file, like I am supposed to know who he is?? Ugh he is such a Madonna!