Joe Elliott got the name of the song when he was sitting in the basement of his London flat. He asked Mutt Lange for some sugar to put in his tea. Lange, in return, asked Elliott if he wanted one lump or two and Elliott said, "I don't care, just pour some sugar on me" and the name stuck.
It reached number 2 on the US Billboard Hot 100 on 23 July 1988, behind "Hold On to the Nights" by Richard Marx. "Pour Some Sugar on Me" was ranked #2 on VH1's "100 Greatest Songs of the 80s" in 2006.
If you're interested in learning more about Def Leppard, check out this post I wrote in 2014.