I'll do one from each region.
Kanto: Blue. It looks like he always wanted to be a Saiyan as a kid, but all the neighbor kids were like "DBZ is for babies!" so he stopped trying to become one, still loving the idea in his thoughts but on the exterior he joined the "DBZ is for babies!" chorus so he wouldn't get made fun of, mellowing out later in life by not being a bully anymore but at the same time not acknowledging that part of himself that once existed.
Johto: Falkner looks like a generic "cool guy" anime character.
Hoenn: Flannery. She reminds me of an angsty teenager. I can just picture her shrieking "MOM, you just don't understand!" and then diving into her bed and sulking while listening to punk rock music.
Sinnoh: Roark. It looks like he doesn't shower. And the reason he doesn't shower is because he thinks not showering is the cool thing to do. He's a friendly person, he just has this odd delusion. He has a small following of kids a few grades below him, who are at an age where they're generally easily influenced by people who are older than them (which is why they're not turned off by his lack of showering; they also think it's cool). He has a big sister who pities him.
Unova: Burgh. He's wearing what looks like 1970s fashion, which always seemed thrown together to me and looks like it feels awkward and uncomfortable.
Kalos: Clemont. That jumpsuit is just...ugh...it makes my eyes vomit...