A word that is almost exclusively used in Northern Ireland.
It is a rather simple insult/comeback, it means 'suck the back of them' with 'them' being testicles.
For
non-Northern Irish
people it is pronounced 'sucka-backy-im'. That's IM as in
TIM.
John: Here mate that's my football,
giz it back ya wank
James: Na mate my ma got me this one
John: Mate, its the same
ball, just giz it back!
James, Na suckabackyem
ye ain't gettin it.