He was drunk. The only way he would ever call her 'Rosie-Posie' in front of the family and not expect her to curse him to Tartarus and back was if he was drunk.

“Can I let you in on a secret?” Rose leaned forward, whispering conspiratorially.
“Certainly,” Scorpius mimicked her and whispered curiously.

“I have no idea what I'm supposed to do for a wedding."

“Honestly Scorpius, how many of us ever actually find that special someone?” she questioned.

Scorpius pointed to the soon to be wed couple, “I've seen someone who has.”
Rose pursed her lips with a small sardonic smile, “Have you found that person?”

Oh this was too precious.
It had taken all of Draco dormant conniving to come up with this and he had succeeded.
See Potter? Not all my plans end in debacles. Just most of them.

“Scorpius?”
Scorpius stared at her, wondering where he had seen this young woman. She couldn't look more than twenty. 

“We met at the Gladrags Fashion show?” She smiled tentatively.
He felt his face flush as he remembered exactly what- or who- he had done that night.

Merlin, when had she turned into such a sap anyway?

Not for the first time in that hour did she curse Scorpius Sodding-I-Have-Bloody-Deep-Blue-Eyes-A-Woman-Can-Swim-In-For-Hours Malfoy.

He nodded, “So I took the old saying by 'eart: If you can't beat zem, join zem.”
As if on cue, a tawny owl flew at her, and held it's leg out with a letter.
“Rose.” He looked at the letter. “What will it be, Rose? Will you try and beat zem, or join zem?”

Scorpius' mask slipped off as easily as oil on marble. “Unfortunately for you, Grandfather, I happen to be in love with Rose Weasley. So I suppose you'll have to add that to the list of many disappointments I've brought unto the Malfoy name.”