There a six different personalities in the games that neighbors can have. A neighbour's personality decided how they will act and what they will say, and possibly how much they are willing to move (away).
 Female only personalities
 Male only personalities
As you can see from the left, a male neighbour cannot have for example a Peppy personality because it is for girls only. This is useful for determining what personality a neighbour is. However, if someone has hacked their town, they can manually change, say, a male jock's personality to a peppy, snooty, or normal personality with the use of a hacking tool called NPC Tool.