Most Ridiculous. Ever.

Saturday was rough. We had a visit from MATCH, which is always a little bit stressful. Especially when it's during lunch and we're then delayed two hours. Which? When you've gotten to work at 8:30, like H, means you're pretty damn hungry.
Once she had left, I--exhausted from standing at the register for two hours doing MATCH stuff--flopped myself onto the stool and hoped the next hour would be uneventful.
A man approaches me. He has a reference book to return. We don't normally take returns on reference material, but since his receipt hadn't been stamped with that message, I was willing to compromise and take the book back. However, when I flipped the book over, the back cover was bent and the corners were bruised.
"I'm sorry, but I actually can't accept this as a return. It seems to have been used and we can't re-sell in this condition." I say this politely.
The man gets very agitated: "I spend at LEAST $4000 a year here. I did NOT use this! It was like this when I bought it."
"I'm really sorry, but I just can't take this back."
He sighs and rolls his eyes at his six-year-old daughter. Right then, the phone rings. I answer it, thinking my conversation with him is over.
One of my managers is calling to see if I need a break. She's heard about the busy morning and is concerned. We have a quick exchange and I hang up. Meanwhile, the man continues to shout at me, saying to his daughter, "Look, she doesn't even care enough to listen to me. She's blabbing on the phone. She's ignoring me!"
And then...he CHUCKS the book across the desk. It smacks me in the arm. I'm too stunned to do anything other than stare at the book as though it has, personally, assaulted me.
He then progresses upstairs, where he asks to speak with a manager. As he recounts my "irrational" and "rude" behavior to J, he also mentions that I ignored him to chat on the phone with a friend.
So he's obviously full of shit.
This is the thing, though. He's lying--I wasn't rude at all, I wasn't on the phone with a friend, I was following company policy, and I really don't appreciate that I was made uncomfortable in my place of employment. The fact that he's lying about my job performance irks me. I'm not some kid running a cash register with a bored expression on my face. I take my job seriously, I'm very engaged with customers, and the fact that I could potentially get in trouble for his LIE is frustrating.
Telling you something you don't want to hear doesn't make me a liar. It makes me a conscientious employee unwilling to be bullied by yelling customers. I have a responsibility to the company to maintain positive customer relations, but considering the fact that he HIT me with a book makes it difficult for me.
What it comes down to is this: I shouldn't have to wonder every morning how I am going to be verbally or physically abused at my job by people I am not allowed to argue with.
Powerlessness is an awful feeling.