Headgirl was a collaboration between Motörhead and Girlschool in 1980, the result being the St. Valentine's Day Massacre EP, though the groups were credited as MotörheadGirlschool on the EP.

The collaboration between Motörhead and Girlschool started in March 1979, when Motörhead began their first big tour with Overkill and Girlschool were their opening act. Lemmy had heard Girlschool's single "Take It All Away" and thought they were "fucking excellent" and liked the idea of girls being in a band. In his opinion, Kelly Johnson was as good as any guitarist that he had ever seen in his life and "wanted to stick it up these pompous bastard guitarists' arses". In late December 1980, Motörhead's drummer, Phil Taylor, broke his neck, preventing his continuing to play, so Motörhead's producer, Vic Maile, suggested they record a single with Girlschool. Lemmy chose "Please Don't Touch" by one of his favourite groups of the past, Johnny Kidd and the Pirates, for the flipside. The bands recorded each other's songs — Girlschool performed "Bomber" and Motörhead performed "Emergency", although Denise Dufort played drums throughout. The record was released on 14 February 1981, as St. Valentine's Day Massacre EP and reaching No. 5 in the UK Singles Chart, it became the biggest hit either band ever had in the charts. On 6 February the bands had been filmed in concert for a Nottingham TV show called Rockstage and on 19 February, billed as "Headgirl", they appeared on Top of the Pops playing "Please Don't Touch". With Girlschool as special guests on the Motörhead 2005 'Inferno UK Tour', Lemmy joined the band at the end of their set at Brixton Academy on 19 November to play "Please Don't Touch" for the first time ever live.