Think of ways that you do things that other people do things differently than you.
Religion- different religions celebrate different holidays, different services (like church), some people aren't religious at all
Backgrounds/cultural identity- people come from all different places, some even from other countries. There are things like languages and foods and traditions that come with it
Social cliques- People tend to talk to those who are most like them, so there are different groups in environments of different people.