In order to get this to sound as much like the original as possible, you’ll need to drop tune to D. If you’re not familiar with drop D tuning, all it means is you tune your low E string (the 6th string) down one whole step to a D, and then adjust the way you play your chords accordingly. You need that string tuned down to a D so when you strike the 6th, 5th, and 4th strings open, it creates a D chord with a powerful bottom end, which is used frequently in this song.

The part where it says D (Dmaj7) is just our way of saying that there is some picking action going on there between a D chord and a Dmajor7. Imagine if instead of playing an open D chord as a little V shape, you just barred across the 1st 2nd and 3rd strings all on the 2nd fret, that would be a Dmaj7. Listen to the song to figure out the picking pattern, this isn’t GreenDayPickingPatterns.com, after all!

For the quiet parts of course you should be palm muting.

Green Day - Whatsername - Chords and lyrics