Green’s Dictionary of Slang

custard n.

[resemblance]
(Aus.)

1. in pl., pimples, acne [the yellow pus such eructations contain].

[Aus]Baker Popular Dict. Aus. Sl.
Tharunka (Kensington, NSW) 6 Sept. 26/2: Acne Problem: I've got a problem. I’ve got blackheas [sic], custard tops, splotches, zits, craters, pimples, ackers, dermatology, pock marks, and acne — What is there for me to do?

2. semen.

[Aus]‘No. 35’ Argot in G. Simes DAUS (1993).
[UK]Roger’s Profanisaurus in Viz Apr. 48: lightning in a bottle n. A photographic art study which captures the moment a gentleman expels his custard arcing majestically towards the face of a beautiful young lady.

In compounds

custard pie (n.)

(US teen) the female genitals.

OnLine Dict. of Playground Sl. [Internet] custard pie n. vulg. clitoris. Used as ‘I would sure like a piece of her custard pie, I would like to chew on a piece of her custard pie.’ So named because of the way the lips come together, not to mention the creamy filling that is issued.

In phrases

clear the custard (v.)

to masturbate, after a long period of continence.

[UK]Roger’s Profanisaurus in Viz 87 Dec. n.p.: clear the custard euph. To have a long overdue wank. e.g. ‘Ooooooh I’ve got balls like boulders. I’d better nip upstairs and clear the custard’.