Disclaimer: Mortal Instruments is not mine.
Smart aleck: a person given to obnoxious cleverness
(Maryse and Alec Lightwood)
Her eldest is the only one in the household with a gram of common sense. He's the one who mediates between Isabelle's passion and Jace's icy rage against the world and he manages his role as the older brother with a maturity beyond his years. He may not be a natural like Isabelle and Jace but he's still a damn good Shadowhunter which he's proven when they go out to do mother-son bonding (in other words, do the only stress relieving she's legally allowed to do that involves killing).
He definitely is Robert's son though and only talks when he has something important to say. He was always a quiet child and was extremely observant about what everyone said which had an unfortunate effect of rendering sarcasm useless. Like when Isabelle's hair had been drenched in some unidentifiable substance after she'd tampered with the bows in the training room. She'd yelled because her floors were covered in the liquid as well and Alec just stood there blinking at her, telling her he didn't know how Isabelle had gotten coated in the stuff and buckets can't fly, Maman.
Jace told her sometimes that he wanted to shake his parabatai so that the normally intelligent boy understood, that, no, he didn't mean that the demon disappeared through a freakin' (he didn't use freaking however) wall.
It was only after when Hodge was asking her children with great exasperation if it was really such a chore to do the work he assigned and Alec answered yes extremely seriously that she realized that he was playing with them. She started laughing manically because he was definitely her son. Her little smart aleck.