Dunhill is a very nice brand of pen. You use the term "dunhilled in" when something is for sure or definite. This term is derived from the saying: I'll "pencil you in"... pencil can be erased but when someone is "dunhilled in" its for sure.
Oscar: Am I gonna see you tonight?
Amanda: I don't know... I'll try to pencil you in.
Oscar: I wanna be dunhilled in.