“Bomb-bomb-bomb, bomb-bomb Iran” is, potentially, a pretty funny line, but McCain didn’t deliver it all that well. From watching the video, it looks to me like McCain hesitated as he was talking because he was worried that he might be being impolitic, and thus his timing was a bit off.
So, was it impolitic? I’m not so sure. It’s not as if the question was “what’s your position on Iran?” The questioner basically asked when the heck we were going to bomb Iran, and McCain attempt to riff off of that. My reaction is similar to Jesse Walker’s take on Reagan’s “bombing in five minutes” joke: “I was a firmly liberal 13-year-old when he said that, but I just couldn’t go along with the condemnations raining down from my side of the aisle — it seemed too much like something I would say if I somehow got to be president.”