Chris Jericho and Brock Lesnar were involved in a legitimate backstage altercation at Sunday's WWE SummerSlam pay-per-view. According to multiple accounts, Jericho was frantic backstage, questioning what Lesnar did in his main event match against Randy Orton. Apparently Jericho felt Lesnar had gone too far and was in business for himself.
When Lesnar heard Jericho refer to the lack of answers as "bulls-t," things got interesting. Brock reportedly told Jericho it was none of his business but he didn't back down. This resulted in Brock pushing Jericho and kissing him on the forehead. According to Ryan Satin of Pro Wrestling Sheet, Lesnar told Jericho, "kiss me back, p-ssy."
Jericho rushed him but Lesnar put his hands behind his back and told Chris to hit him or kiss him. Multiple wrestlers, including Triple H, broke them up. Vince McMahon told Chris to be more professional, when Chris accused Brock of being unprofessional for shooting on his co-worker. Vince told Chris it was a work and asked what was wrong with him.
Things eventually cooled down and both Lesnar and Jericho went their separate ways.
ProWrestlingSheet.com has further details of the altercation available at this link.