I’ve been mildly obsessed with The Clash’s Straight to Hell since Cover Lay Down (one of my favourite mp3 blogs) posted a batch of cover versions of it. This riff only crops up briefly in the original song but was made more recognisible thanks to it’s use in M.I.A.’s Paper Planes. By the by, if anyone invites you to their serial killer warehouse, probably best to politely decline.
It’s important to make sure the notes in this riff are played staccato (i.e. they only sound very briefly). The easiest way to do this is it to fingerpick all the notes and mute them with your picking fingers.