boss called me a fat fucking whore..

I work for a small mechanic shop, a partnership LLC. I have two bosses, whom are both owners. One is incredibly nice and had always been that way, one is far from that. --

We have a pretty relaxed workplace, jokes and mild pranks just to keep it fun. I think it's gone to far honestly. -- Here's the story. 

My boss (the rude one) called me a "fat fucking whore" I kind of shooed my hand like you would if you were telling someone to go away, but I accidentally hit him in the face. I apologized and asked if he was fine, making sure he knew I didn't mean to. A bit later, maybe a minute he back handed me in the mouth. He didn't break the skin or anything like that but it hurt pretty bad and honestly, it made me cry. While I walked away slightly crying, he was laughing at me. It's been a week now and there is still hostility towards me from him. Without telling me or my other boss, he put my job on Craigslist. It's just crazy, I've even here 3 years out of the 3 and a half years that they've been opened. My questions is, is it too late to tak legal action? My other boss and mom suggested I sued. With the time frame, would it make a difference, should I quit? I'm just confued. -- I also confronted my other boss about it. He gave me the rest of the day off and has told me to do whatever I need to feel comfortable