Each character has a personality. There are 8 personalities. Male villagers have four (cranky, lazy, jock, smug), and female villagers have four (snooty, normal, peppy, sisterly).
Cranky villagers will sometimes seem like they're much older than the rest of the villagers. Sometimes talking about back pain of standing too long, or being annoyed by other villagers, and being surprised if you have good taste in things or take initiative.
Lazy villagers are easy to figure out. They like talking about bugs in their house. Sometimes they'll mention that they feel sleepy.
Jock villagers tend to talk a lot of about muscles, working out, being confident.
Smug villagers will say something that comes off as rude, but then pretty much say they're joking with you. They even think highly of themselves.
I have no idea how snooty villagers act since I don't have one.
Normal villagers will be sweet to you.
Peppy villagers are very excited a lot of the time and will talk about being a star or something.
Sisterly villagers are kind of like normal in a way. I haven't really figured that one out yet.