I don't get it, they start off booing him then they suddenly love him?

Honestly, I thought the guy was a really good singer. I dunno why they even booed him in the first place. The fact that they did doesn't reflect well upon them, nor does the fact that they randomly started cheering for him halfway through the song. Honestly, if you don't like his singing, you don't have to be an ass about it, and if you all of a sudden change your mind... Why'd you even think it was bad in the first place? There really wasn't much difference between the beginning and the end. Like I said, I thought the whole thing was really good.

I don't understand these kinds of people, so if someone can answer these questions, I'd greatly appreciate it.