You can start by avoiding things that would make you seem abnormal. Like, avoid hanging out with strange friends. Try to do things that most of your classmates are doing. You can also try to talk to the guy to find out why he thinks you are crazy.
"Normal" is just a setting on the washing machine. But you can tone down the swings in your behavior. Ask your friends to encourage you to tone it down with them so you don't intimidate guys who aren't comfortable with your high-energy self. And perk up a little in school so there isn't as big a difference between you with friends and you in school. And don't do crazy things just because they're crazy. Find a little focus. Do the *right* crazy thing every now and then, stuff that will make people think "wow, that was amazing!"
well if you really want to... When talking to him try to stay on topic, not like: Guy : So.. I saw ( insert thing ) .. You: unicorns. 0-0 Don't make really odd jokes only you will get.. Don't do really random things out of the blue Try wearing clothes that match and are not to exotic. Try to be calm. .-.