a regular winter swimmer

An individual who actually likes swimming in spanner water.
an aussie institution since the 1930s
icy pole
a frozen lollypop
an odd, interesting, or well-known person
Often reported as a well-known racing identity when referring to a suspected criminal.
aussie slang since the 1870s
idiot box
of a suspicious nature
a small-time confidence trickster
Memorably revived by Peter Carey in his novel of the same name, published in 1985. It's origin is uncertain, possibly from pig Latin or backslang.
underworld slang of the 1940s
in a tick
very shortly
in fine feather
full of vitality and spirit
in it
anything done in the company of others
The it that you may be asked to be in may be physically or alcoholically exhausting.
Will you be in it?
Go on, be in it!
Goin' fishin' next Tuesday—be in it?
in like Flynn
assured of success in an enterprise
 Originally meaning assured of a sexual conquest. Referring to aussie actor Errol Flynn, well‑known for his sexual adventures.
Interestingly, this term has been in use in the USA since the 1940s, but only in the non‑sexual sense.
wwii slang
in the chair
the person buying the drinks
in the know
having inside information
in the raw
in the shit
in trouble
Also, in deep shit  meaning in serious trouble.
in the sticks
in remote rural areas
in the wars
going through a period of trouble, illness, or the like
in two shakes
in a short time
irritation, annoyance
iron lung ∼ wouldn't work in an iron lung
extraordinarily lazy
it's the

Illustrated Dictionary of Australian English