This is what happend to me, what would you do?

Ok, i walked into work one day and in the back room where the schedule is posted there was a little note with a fake penis on it, there was an arrow that said my actual size. i wrote a note with it and put it in the safe for the management to find. Three days later i got a phone call from a co worker saying he was gonna beat me up for what i did about the note. so i went down and talked to my employer about the sitiuation. He told me that it was just a joke and that i was being childish about it. in the middle of the next week i was fired. my employer never called me to tell me a fellow co worker called and told me the news. See i'm really stuck i don't know what to do about it. but i do have a picture of the note on my cell phone. please help me figure out what to do.