The word (or sound effect, depending how you look at it) you say when you're mildly impressed by your girlfriend's appearance, but don't want to get all mushy about it. You know, you cool dudes.
*Sophia comes down the stairs in her new dress*
Michael: (oh, geez, I don't want to be mushy about this. I'm a cool dude. How can I be cool and still give her a compliment? Oh! I know!) "Daaaang!"
ddaaaanng is a word you obnoxiously say out loud, yet under your breath when you're annoyed or fed up with someone or a certain occurrence. It's typically used comedically when your fed up with your infuriating friends.
Some girl bumps into you
"ddaaaanng"
Someone walks super slow and front of you
"ddaaaanng"