Reasons to organize a party

Do you really need a reason to organize a party? If you think yes, here are some ideas.

It's you birthday. Invite your friends to your birthday party.
It's your names day.
You graduated. Or you just passed some more or less important tests.
It's one, two, five or ten years since you graduated from school, college or university. It's time for a reunion.
You are going abroad. Invite your friends to a farewell party.
A friend of yours is going abroad. Organize a party for him at your place.
You have some visitor from abroad. Your friends will be curious to see him or her.
You just moved into a new house or apartment. The same is true if you are about to move out.
It's spring break or fall break.
Your favorite basketball (football, soccer, baseball) won a championship. (Make sure you that you are supporting a winning team. That'll guarantee that you'll have more reasons to organize a party.)
It's summer and it's your vacation.
You have been promoted, hired or fired at your job.