I Must Be Crazy

I don't give a fuck about my job.  I don't give a fuck about my life.
Today is a day off.  The last few days at work have really sucked.  You see, if I see someone that has some of our merchandise approaching the exit of the store I work at, and I can see that they didn't buy it in that area of the store, I'm supposed to ask to see their receipt, even if they are carrying the stuff in one of our plastic bags.  Obviously, someone could grab a bag, put stuff in it, and walk out while acting as though they bought it.  Although, as I've been obsessively thinking about the events of the past few days, I realize that I've never seen a particular head cashier, who's been working at this store longer than me, ever check a customer's receipt, and that's part of her job.  She spends a lot of time standing by the main exit.  Regardless, she received an award at the last store meeting, because she "seems to never have a bad day."  Maybe she'd have more "bad" days if she was confronting people who were trying to leave the store.  She's also hot as hell, which would explain why she'd get away with anything.
A few days ago, I asked to see a customer's receipt and he was a total prick to me.  It's happened before.  It's not fun.
But, two days ago, a couple of guys exited the area of the store where I was working holding plastic bags with stuff in them.  I didn't ask to see their receipts.  I don't always do it.  I don't like doing it, because I don't like it when people are rude as hell to me, as they sometimes are when I do that.  Later, those guys came back: one of them bringing stuff in one of our bags into the store.  This time, I would confront them.  As they were leaving, I walked up to them and asked to see a receipt.  One of them said, "That's rude" to me.
"That's store policy," I replied.
He got very angry very quickly.  "Don't you see he's got a bag?" he yelled at me.
I walked away and said something about how I don't appreciate being yelled at.  I think his buddy tried to get him to leave as he was leaving, but he said, "No.  He might call the police."  He aggressively got very close to me and continued to yell at me.  I was so worried he was going to hit me, that I backed away from him a few feet.  He pulled a receipt out and yelled, "Do you want to see it?!" multiple times.  Finally, a coworker heard all the yelling and walked over to me, so that he was standing next to me.  The asshole left soon after.  Then I heard one of them laughing loudly outside the building.  I suppose he was laughing at me: the pussy.
I've since realized it's stupid to be a corporate tool.  I should put my ass on the line, I should put my health and safety at risk, for the sake of the owner, who must be rich as hell, highly-paid executives, or wealthy shareholders?  That's crazy.  We have a concrete floor.  Someone could knock me out, and my skull could fracture after it hit that unforgivingly hard floor.  It would be fine if I was murdered; that would be great.  But what if I was crippled?  What if I was injured so badly that I was paralyzed from the waist, or the neck, down?  Then I'd really have a reason to bitch and moan. 
So I need to be smarter about this receipt-checking business.  I should probably ask to see it while I'm behind the counter at least, so there is a barrier between me and him (or them).  Of course, someone could go around the counter, or throw a punch over it.  It should be a judgment call: based on how threatening the person (or people) appear to be.  Most of all, I need to protect myself.  This store rakes in millions of dollars a year, despite what people steal from it.  I need to protect my own skin more than other people's money.