headbanger

noun

1. One who dances by violently shaking the head in time to the music.
2. (broadly)One who enjoys heavy metal (rock) music, to which this sort of dance is usually performed.
3. A violently deranged, extreme or fanatical person; a nutcase.
4. A silly or eccentric person.
5. (UK)A political hardliner, especially an obstructive one.

   “We would therefore paralyse ourselves for no good reason other than the propagandistic appeasement of the Daily Mail, the Sun, my noble friend Lord Hamilton and a few other headbangers in the Commons on the Conservative side.”

   “Corbyn's lack of ambition would turn out to be one of his great selling points. He was the man at the margin: a headbanger for most and a man of principles for a few.”

   “Even the Brexit headbangers of the European Research Group rolled over like pussycats.”

6. (Northern-Ireland)A person who engages in street violence, especially in support of a political group.

   “We also had a heavy crew of home-grown headbangers who were likely to get involved in any IRA - UVF battles. It would not have taken much to tip Scotland into the serial sectarian violence that was rife in Belfast and the surrounding areas.”

   “John had a nasty side to him – he wanted to see the handiwork, if y'know what I mean. That sorta thing didn't interest me. He had a lot of headbangers around him but that was his style. He wanted to outdo the UDA – he hated them with a passion.”

   “In the Long Bar, you had 'Chuck' Berry and his mob. You had Lenny Murphy and his mob. And you had them in the Rex Bar, and you had them in the Windsor Bar. All different, separate groups of all headbangers. Now, from time to time, the leaders would have given them instructions to carry out certain murders or given approval for certain murders.”

7. A kind of chin-up or pull-up exercise where the head is kept in line with the bar.