Worked security at a factory that made kitchen appliances. It wasn't his first day, but it was his first shift by himself.
There's a gate at the front that you lock when you go on rounds.
Dude chooses to go on a round 5 minutes before shift change for the factory workers. He gets a call on company cell that folks are at the gate. Instead of coming back, he tells them to wait 20 minutes so he can finish his round.
20 minutes where they won't be getting paid.
Second in command big boss of the factory is out there checking IDs and directing traffic when dude gets back from his round.
Now this dude is nice. Genuinely one of the nicest people you'll ever meet. Old union rep, shirt off his back type. Tells guard not to worry about it, all's good. Just time his rounds better next time.
Guard starts screaming at him about how he had no right to undo the lock, to get out of here, he'll handle them, and if he wants to make them wait that's his right. Boss man tells him to chill out, he won't get in trouble, just go do his log and then he can take over checking IDs.
Guard pulls out, in one hand, a mag light flashlight he was told not to have, and in the other chemical spray that's illegal for a guard to carry without certs (which he didn't have), and this is an unarmed site. Threatens to ""arrest"" him. When boss pulls out his cell to call the guard company, the guard sprayed him and knocked his cell onto the ground, and kicked it across the parking lot, breaking it.
Needless to say, he was fired. Boss didn't press assault charges, but we nearly lost the contract.
Not just mall cops, it's just people in general in any position of power. When I was young I used to host game servers for a community I created and liked to have a decent amount of people to administrate them and keep the games fun for everyone. There were people playing for months and always seemed reasonable and level headed and I'd see if they would be interested and most jumped at the chance to be more involved in the community. Every once in awhile though those reasonable and level headed individuals once they got some measure of authority went absolutely crazy and there's no indication of who it would be. People can be the exact opposite too, they clown around taking nothing seriously always trying to push boundaries, but then you give them some responsibility and suddenly they are the most responsible person you've ever met, they just needed a chance to show it.
Depending on the state, security guards do have some power. In Tennessee, guards can be bonded, which effectively makes them cops.
In Virginia, security guards have powers of arrest, so they're not cops, but can legally arrest and detail you, to include handcuffing and up to lethal force in certain situations.
But to your larger point, it's a power trip. I worked security for 10 years. Most guards do not give a fuck, they don't want to do anything more than the bare minimum, and will passively just sit there while people steal and shit.
But occasionally you get a power tripper. Someone who went into security because they couldn't hack being a real cop, so they decided to become a rent-a-pig. This is usually seen in people 60+ or under 25.