Green’s Dictionary of Slang

a general exclamation.

1973		Sun. Times Mag. 30 Sept. 36: Most of them say ‘rassklat, I come over here, I want some money to go back home with’.
1983		J. Milne London Fields n.p.: Plenty of third-world shouting going on, y’raas, Babylon, raas claat!
1991		L.E. Adams Jam. Patois 59: Ras or Raas: backside, rump; a common curse is to rass! or rass clot!
2000		N. Hopkinson Midnight Robber 52: ‘Rasscloth,’ Antonio breathed in amazement.
2011		T. Powers On Stranger Tides 90: ‘Raasclaat,’ he swore softly, then rumbled, ‘Ah cain’t quite get the faastie bastards to behave’.
2011		J. Cornish Attack the Block [film script] 87: PEST Aw man, that’s ours! Worth bare P’s! Rasclat...