Green’s Dictionary of Slang

1. to indulge in violent sex.

c.1951

N. Algren ‘Watch Out for Daddy’ in Entrapment (2009) 134: Who’s the one friend a hustling broad’s got? [...] Who’s the one don’t let you get trapped with the monstering kind?

2. to harass a woman in the hopes of seduction.

1967		‘Whisper All Aussie Dict.’ in Kings Cross Whisper (Sydney) xxxvi 4/2: monster: Make unwelcome passes at a female.
1986		R.G. Barrett Godson 278: [S]he’s all my way. No need to monster her.
1999		R.G. Barrett Wind & Monkey (2013) [ebook] [S]he even got monstered by drunks walking back from the toilet. Just keep looking boys, nodded Les. But don’t touch.

3. to assault sexually.

1986

R.G. Barrett Real Thing 146: He’d either do something he’d regret or just straight out monster her.

4. to attack (verbally rather than physically), to pressurize.

1983		Sydney Morning Herald 5 Mar. 13/6: Ian Macphee was in trouble for saying something good about the prices and incomes policy while the Prime Minister was monstering it, although at times Fraser seemed to have trouble deciding whether it was a monster or a mouse [AND].
2007		S. Maloney Sucked In 65: ‘Charlie Taylor’s bum boy,’ he’d chorus. Low-grade monstering, it might have got a rise out of a first-year apprentice.

5. (Aus.) to subject to a severe defeat.

1999

P. Temple Black Tide (2012) [ebook] Well, the bookies have been monstered here, ladies and gentlemen.