an individual, usually a man, that you are involved with. He is usually not a boyfriend, yet he is more than a friend, sex is typicaly involved. Yet his intelligence is limited and rather than let everyone know you are banging an idiot you refer to him as"dum dum" in an effort to save face and protect his identity and your image. You do not call him dum dum to his face, you only use this term to describe him when speaking with your friends.
Jas: "What did you do last night?
Mia: "Dum dum cam over last night."
Mia: "Remember the guy I told you about, dum dum?"
Jas: "ohhh yeah."