Matt Jender

Showing off his band: His greatest pride is Löded Diper. If he likes you, the first thing he'll do is invite you to a rehearsal in his garage (even though it sounds terrible) or give you an official band t-shirt he made himself. He'll want you to watch him play the drums because he thinks it looks incredibly cool.
Bad boy attitude: He would try to act more mature or "rebellious" than usual when you were around: leaning against a wall, crossing his arms, speaking in a lower voice, or pretending to be tired of life
Even though he acts tough, inside he's probably super nervous. To hide it, he'd likely use sarcasm or mean teasing (very much like an older brother), but in a gentler tone. If he teases you in a friendly way, it's his way of getting your attention.
His wires would be crossed. Rodrick isn't exactly the sharpest tool in the shed; if you talk to him about surprises, he'd probably freeze, say something stupid, or accidentally break something in his clumsiness.
She would use her sister: She would use her younger sister to do the "dirty work." She would order her sister to find out what you like, what music you listen to, or if you're dating anyone, all under the threat of making your life miserable if you say a word.
Zero shame in front of his parents: If you're at his house, he'd completely ignore Susan and Frank's rules to show you that "he's in charge," even if five minutes later his mom scolds him for not cleaning his room and ruins his whole tough-guy moment.

The "anti-posture": His style isn't just about his clothes, but how he moves. He's always hunched over, with a bored expression, a total lack of interest in the world, and a defiant attitude towards his parents.

He has a shag or long indie-style haircut, messy and a little greasy, as if he had just woken up from a three-hour nap.

Band T-shirts: He always wears dark (black, gray or navy) short-sleeved T-shirts, often with the logo of his own band, Löded Diper (Celebbro Diper), or with rock/metal style graphic prints.
Layers upon layers: A classic of his style (especially in live-action movies) is to wear a short-sleeved t-shirt over a long-sleeved striped or plain-colored t-shirt.
Baggy or worn pants: He usually wears dark jeans, slightly baggy or sagging, which reinforce that "I don't care about anything" attitude.
Accessories: Leather bracelets or spikes, black fabric wristbands and, sometimes, very subtle black eyeliner when she is going to play with her band.