The thing about the likes of Hunter Mahan, Matt Kuchar and Dustin Johnson is it always seems like they're the chilled out ones on the golf course. Yeah, they might get pumped up after certain shots, but for the most part they go about their business on the golf course.
That is, unless you're yelling something in their backswing. Mahan was on the 18th hole, 1-down and in need of something magical. He's standing over his second shot, about to take the club back and someone yells. He didn't appreciate it.
Hey, can't blame the guy, I'd probably get mad too. Sadly, getting heated didn't help. Mahan and David Toms lost their match to Charl Schwartzel and Retief Goosen.
h/t Devil Ball