I'm just going to come right out and say it: I struggle with this one. As a matter of fact, I didn't even realize it was a problem—or that I was doing something wrong—until about this time last year.
I'm talking about treating people like objects.
Stop yelling at your screen. I mean grammatically.
We see this all the time in speech and writing, and even though it doesn't sound wrong, it is.
Incorrect
Are you the one that keeps bursting into flame during class? Great excuse to leave a boring lecture!
"That" is used for objects, not people. A person isn't a "that," they're a "who."
Correct
Hi, I'm the Dean of the department. Are you the student who spontaneously combusts during lectures? I'd like to see you in my office. Bring a fire extinguisher.
It's especially hard to remember if you're in the middle of an argument.
Incorrect
"You want to see me?!? I can't help it if I start on fire when I'm tired. YOU'RE the one that hires boring professors!
The rule goes the same for plural—"people" or "persons" aren't the ones "that", they're the ones "who."
And there you have it. Now you can stop objectification one sneaky that at a time.