I see the relationship between these two as very caustic.
Backtalk!
Duo brought a lady home for the evening; rather, the end of the evening. His son was there to meet him, angry he didn't call about staying out late. The dummy had forgotten his key, and since Duo Jr. didn't feel like being robbed in the dead of night, he waited up for him. When they made eye contact, at first, nothing was said. When the woman excused herself to use the facilities, it was time to strike. "Have you been drinking?" Duo scolded his father.
"Yes and Daddy's getting laid tonight, so scoot off to bed," he said, soused.
He folded his arms, ready to deliver a verbal lashing. "Kay, if you make me stay up so you can come home like this again, I'll lock you out till morning; second, I'm sixteen, I don't have a bed time; and last, stop the third person baby-talking, you're a grown man. Trust me when I say, if you don't smarten up, I'll make it so you'll never get laid again."
He was trying to be nice about it. Duo stared his bastard child in the face and said, "You cock block me you little shit and I'll beat your ass."
Blank stare, "...well put," he said and scooted off to bed as told. A physical lashing was far more menacing than anything his sharpened tongue could dish.
Why? Because the way Duo introduces his son for the first time in Frozen Teardrop, he basically says, "This is my awful child, I raised him poorly."
He's being sarcastic, but he really says, "This is my ray of sunshine." The way it's spelled in the book, the character used to spell 'sunshine' is swapped for one used in the word 'terrible'. It's a pun, and it's awesome. ^^
