Blink wrote this song and “Fuck a Dog” as a symbolic big middle finger to MCA Records. They noted an immense pressure from MCA to write a carbon copy of Enema of the State, so they decided to play a prank on them as Tom DeLonge detailed in 2012 for Music Radar:

I remember the label came down to hear the big follow-up and those were the only songs [“Fuck a Dog” and “When You Fucked Grandpa”] we played them. Oh my God, they lost their minds. We had this song about fucking Hitler — we changed it to ‘When you fucked grandpa’, but it originally was, ‘When you fucked Hitler did he tell you that he loved you?’ They lost it.