I'm the worst person on the beach
How did you end up with that conclusion?
I threw sand at people who were relaxing on the beach
Throwing sand at people who are minding their own business could be considered assault which is against the law. You are behaving like a bully and you could end up being arrested for your bullying behavior.
I was only trying to have a little fun.
You may have had your fun but others were hurt and harmed with what you did and that is never okay, as you shouldn't disregard others' feelings specially if you're harming them for your own benefit. You should apologize to those people who you threw sand with and promise to them you'll not do it again.