knacker

A deeply derogatory term for an Irish Traveller. It's a slur — full stop — rooted in the historical association of Travellers with the knacker's trade (slaughtering old horses for hide and bone). Considered hate speech by the Traveller community and equivalent in weight to other ethnic slurs.

By extension, a broader insult for someone seen as low-class, scruffy or anti-social — overlapping with 'skanger'. This usage is still offensive because of where the word came from, even when the speaker isn't aiming at Travellers.