Can I get in trouble for saying something racist on twitter towards someone?

[Kaleb]

it would not go to trial
they cant prove you said it and not someone else who got on your account
""Congress shall make no law respecting an establishment of religion, or prohibiting the free excercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances." -US Constitution
It is not illegal to say racist things. It is illegal to commit actions against people out of racism, or to deny them opportunities because of their race/religion.
Most establishments (such as twitter) have rules of conduct against racist remarks and and can ban you or kick you out for such things. Nothing can be done if you didn't threaten him. Even if you did it'd be too hard to prove anything in court if you said it wasn't you.
Good thing we're American and have freedom of speech.