Well he used a naughty word which he shouldn't have. He could of course have said something a little less hostile. Like "are you going to sing this song then?" or something.

But I've been tempted to heckle when I've experienced people hogging other people's time in situations like that. it's inconsiderate.

Like when you're at an Open Mic and you get three songs each: there's always one (usually a pony-tailed middle-aged guy with an expensive guitar) whose first song is about the length of other people's three. And then his second's even longer. And then his third... you get the idea.