P!nk on VH1's Storytellers about song lyrics 
and more specifically "Who Knew"

"He was one of my first friends — this is gonna sound awful, but true — to die of a heroin overdose. And… he was a pretty special man, he was captain of a football team. Not who you would expect. So when I wrote this song, it was sort of ‘If someone told me three years from now you’d be long gone, I’d stand up and punch them out. ‘Cuz… you said forever.’

That’s what it meant for me, but each year, almost it’s taken on a different meaning. Whether I lost someone else — I lost my dog… it became about Elvis for a while. Every time you’d see a show where I’m crying it’s basically been about a new person. It was about my grandmother who passed away. It just keeps on taking — It’s always new to me and for that reason I think it’s a special song in my life.”

(Source: everythingiveseentwice)