Happy Birthday OP! That really sucks, I hope they didn't go too hard on you.

You said "hard on".... Huh-huh-huh....

Party at home, you get in less trouble that way.

I'd find that much more amusing if your name was talented69.

Welcome to the other side of adulthood. Accountability. It's a bitch.

Not off to a good start, bro!

Welcome to the Wonderful World of Adulthood(tm)!

With great power comes great responsibility.

I got two letters for you: AA

Just because you can drink legally now, doesn't mean that you should do so excessively.

My 21st birthday I went to Disneyland. Can't get in trouble with Disneyland.

either the party was outdoors or your drunken self took a walk.
need to know how you got arrested? we're you not at the party?

*were

How is that even illegal? Are you not allowed to walk home from bars or how do they enforce that?

They were probably being a public nuisance. They will arrest someone if they're obviously drunk. They could endanger themselves or others.