Dear Justin Bieber, get yourself a catcher's mitt and some sunglasses, because your ex Selena Gomez is throwing shade your way -- and on national TV to boot.

When on 'The Late Show With David Letterman,' Gomez dissed her ex during the interview.

When Dave asked the singer-actress if she was dating any boys, she said, "No, net yet."

He egged her on, saying, "Last time you were here, you were with a Justin Bieber," which she replied, "With a Justin Bieber?"

Still, the host bantered back, "That's not going on now?"

"No, I'm single, I'm so good," she said with a uncomfortable, gaze-averted giggle. Clearly, Sel doesn't like talking about this topic, but that didn't stop her from winding up and hitting her ex below the belt.

"The last time he was on, he and I got into a conversation, he said something and I said something, and he said something and I made him cry," Letterman said. (Letterman and the Biebs had semi-argued about tattoos.)

That's when Sel tapped his desk and said, "Well, then that makes two of us," with a very proud-of-herself stare and she and Dave did a fist bump, as charter members of the "We Made Justin Bieber Cry" club.

Ouch. The Belieber nation is about to slay Gomez. Like suh-lay.

She shouldn't have done that.

You wouldn't like Beliebers -- all 75 bazillion of them -- when they're angry. They might not turn green and rip off their shirts like Dr. Bruce Banner, but they do tweet bomb and social media stalk with savvy regularity. We certainly wouldn't mess with that corp of fans, as they have the reach, scope and ability to organize and sink 'Spring Breakers' in their sleep. They broke the Internet, for God's sake. They can certainly attack an indie film.

Consider yourself warned, girl.

We must say, though. Sel didn't look comfortable dissing him, but she also looked sorta smarmy and smug, like she practiced saying that in the mirror.

It wasn't nice. But it was pretty sassy.