Green’s Dictionary of Slang

stiffie n.

also stiffy
[stiff n.1 ]

1. an erection.

[NZ]G. Slatter Pagan Game (1969) 71: There was [...] Long Tack Samuels, Stiffy Cocks.
[UK]Monty Python ‘Meaning of Life’ 🎵 It’s swell to have a Stiffy, / it’s divine to have a Dick.
[UK]K. Sampson Powder 456: He was getting a stiffy.
[UK]Observer Rev. 25 Jan. 11: He massages himself into enough of a stiffy to somehow ram it up.
[US]S. King Dreamcatcher 581: Why such an awful dream would give a kid a stiffy God alone knew.
[NZ]McGill Reed Dict. of N.Z. Sl. 200: stiffie/stiffy Erect penis. ANZ.
[UK]Guardian Rev. 6 Aug. 13: He calls his penis [...] ‘full length’, ‘stiffy’.
[Aus]P. Carey Theft 93: A great stiffy, throbbing like a sock full of grasshoppers.
[Aus]D. Whish-Wilson Old Scores [ebook] Their chubbies hadn’t faded, which was a good thing. In all his years, Swann had never seen a man with a stiffie throw a punch.

2. an invitation.

[UK]Barr & York Sloane Ranger Hbk 159: stiffy n. Engraved invitation card.
[UK]Observer Rev. 22 Aug. 14: You can understand being a bit bereft of stiffies on the mantelshelf.

3. see stiffy n.1 (1)

In phrases

crack a stiffie (v.) (also crack a stiffy)

to get an erection.

Adam ‘What Michael’s Forgetting’ posting 18 Apr. at 4BitterGuys.com 🌐 He can crack a stiffy like fury when he’s up for a challenge. And do you know why? Because He’s a bloke, that’s why. He has a man’s needs. If His fists weren’t nailed to that plank of wood He’d be up there, hammering away like there was no tomorrow. Mind, I wouldn’t want to be the bloke nailed to the cross in front of Him. That’s some holy water I could do without, thanks very much.