It all started when the model posted a photo on Instagram with a friend, writing, "glad to have my Aussie back."
He responded by saying, "ur friends hott hailey haha," then adding "But ur hot 2 😊😊" and writing the nonsensical "Carrot."
While we're definitely shocked that he called her "hot," we love that she responded with her own sassy Instagram comment! After he posted a shirtless pic, she responded by sarcastically calling him "fat."
They've been caught getting cuddly in the past, but they're definitely teasing each other in a flirtatious way!
Of course, since Selena Gomez is reportedly getting closer to Zedd, we think Justin might just be jealous. He's apparently upset that they're dating because he knew the "Break Free" music producer first, so he might be using his close relationship with his bestie to raise some eyebrows.
Do you think Justin and Hailey are dating or just flirtatious friends? Is he trying to make Selena jealous? Let us know in the comments!