At my 2nd job this douche won't leave me alone and management does nothing

I work at a restaurant for my 2nd job and there is a guy who comes in a lot and he and his girlfriend are friends with our GM and our service manager outside of work. The guy is a 24 year old unemployed loser who from what I have gathered makes his money dealing drugs.

One night I got him kicked out by another manager(not the 2 who are friends with him) because he was slapping our 16 year old hosts on the arse when they were walking by and I reported it. Ever since he has come back in and harrassed me/tried to stir shite up with me about it each time he comes in. I can't do anything to stand up for myself because otherwise I will get in trouble.

But a couple weeks ago he tried to do this in the parking lot when I was off the clock and not on the property. So I stood up for myself and fought back, and of course like the coward he is he skimpered back to his girlfriends car and locked the door as I told him to face me like a man. Total coward and pussy. But I felt like I made my mark and it was over with.

But he comes in last night and lied to our managers that I ran food to his table and slammed his plates down spilled his honey mustard dressing and drinks, none of which was true. Of course our managers who are friends with him believed him and threatened to send me home, write me up and suspend me. I pleaded it was not true and they didn't believe me. I didn't get sent home but ever since this guy has started harrassing me I have fallen out of favor with our management despite me minding my own business. I used to get the best sections and everything but not anymore. They clearly favor this guy over me and I don't get the benefit of the doubt.

After he left last night he threw his to-go box of food and honey mustard all over my windshield on my car and its still there since it is smeared everywhere and I need some chemicals to get it off since water isn't doing the job. Anyway I told our managers this and they didn't believe me and said it was probably some bored teenager. They are defending this guy at every turn and I am sick of it. They let him harrass me in their restaurant and make excuses for him outside of it. Quitting isn't an option since I like the extra money and they do a good job working with me on hours with my other job but I need to know what to do to put an end to this.