Green’s Dictionary of Slang

arsed adj.

also assed
[arse n. (1)]

1. bothered, concerned, e.g. I can’t be arsed to do it.

P. McCartney in H. Davies Beatles (1968) 131: If they can’t be arsed awaiting [sic] for me, I can’t be arsed going after them.
[Ire]G. Patterson Burning your Own 88: Don’t forget who it was who organized the building of all this when you were too sulky to be arsed doing anything [OED].
[UK]Guardian G2 1 Oct. 13: They will [...] supply the same service to any other else who can’t be arsed to set their video.
[Ire]P. Howard Miseducation of Ross O’Carroll-Kelly (2004) 95: I couldn’t be orsed telling Kenny.
[UK]W. Self in Guardian Rev. 7 Apr. 3: My writing room is very much as anyone would have envisaged it – if they could’ve been arsed.
[UK]K. Sampson Killing Pool 15: Gang of little divvies them, love. Couldn’t be arsed with them .
[UK]A. Wheatle Crongton Knights 272: The sausages were a dose undercooked — I couldn’t be arsed to point it out.
[Aus]G. Gilmore Headland [ebook] Murdoch [...] thought about the chances of bullshitting her. Possible [...] if he could be arsed.
[Ire]L. McInerney Blood Miracles : ‘He can barely be arsed preserving it’.
[Aus]A. Nette Orphan Road 161: ‘Leigh got rid of her child with Mundy because she couldn’t be arsed looking after it’.

2. fed up.

[UK]K. Waterhouse Soho 131: I’m totally arsed with this liner talk.

In phrases

arsed up (adj.) (also assed up)

confused, mixed up.

[US]J.L. Kuethe ‘Johns Hopkins Jargon’ in AS VII:5 329: assed up — mixed up.
B. Hrabal Closely Observed Trains 142: [film script] My future is all arsed up! My beautiful inspector’s badge shot to pieces!
[US]H. Rawson Dict. of Invective (1991) 25: assed up. Confused, muddled; a euphemism for ‘fucked up’.
K.J. Harvey Town That Forgot How to Breathe 214: It was always interesting to read about how mainlanders got everything all arsed-up about Newfoundland.