Nick Kyrgios has been known to rub his opponents the wrong way. But he went a little too far Wednesday with some out-of-bounds trash talk.

The 20-year-old Australian faced off against French Open champion Stan Wawrinka at the Rogers Cup in Montreal. In the midst of a back-and-forth first set, the two players briefly crossed paths near the net.

That’s when Kyrgios dropped this bomb. (Warning: Kyrgios’ comment is slightly NSFW.)

Kyrgios appears to tell Wawrinka that his girlfriend slept with Australian tennis player Thanasi Kokkinakis, adding the line, “Sorry to tell you that, mate.”

After the match — which Kyrgios won when Wawrinka retired because of injury — Kyrgios admitted to his jab.

“He was getting a bit lippy with me,” Kyrgios said, via For The Win. “Kind of in the heat of the moment. I don’t know. I just said it.”

Wawrinka apparently heard it, too, because he took to Twitter early Thursday morning to address the issue. Needless to say, he wasn’t happy. [tweet align=’center’] [tweet align=’center’] [tweet align=’center’] [tweet align=’center’]

Not cool, Nick. Not cool.

Thumbnail photo via Jean-Yves Ahern/USA TODAY Sports Images