can I get charges pressed against me for talking bad about someone on a social media site?

Libel is a published false statement that is damaging to a person's reputation; a written defamation. 

Slander is the action or crime of making a false spoken statement damaging to a person's reputation.

In this day and age of how quickly chats / tweets / statuses are shared on social media, it is pretty stupid to slam someone on social media.  My advice - if you don't have something nice to say about someone, don't say anything at all. Ever. Remain silent. That way, you have nothing to worry about.

www.legalmatch.com/law-library/article/defenses-to-libel-and

If you're 💩 talking no. Back and forth name calling no. Judge Judy says you can say anything as long as it's a known truth. You can give an unfavorable opinion or review.

If you deliberately, maliciously and viciously lie on someone then yes you can be sued. Arrested no.

Making terroristic threats you most like will be arrested.

Never post anything on the Internet you don't want to follow you until death and your great-grand children will see.