sideways, adj. — Green’s Dictionary of Slang

sideways adj.

(US prison) eccentric.

2002

(con. 1998–2000) J. Lerner You Got Nothing Coming 84: A sideways fish like you won’t last two laps without someone planting a Christmas tree in your chest or slocking the shit out of you.

SE in slang uses

In phrases

go sideways (v.)

1. (UK Und.) to commit a crime.

1899

C. Rook Hooligan Nights 57: The slavey was awright [...] She never went sideways.

2. to become diffcult, problematic.

2006		D. Winslow Winter of Frankie Machine (2007) 45: You’re sideways with Vince Vena? [...] You do have a problem, mid.
2013		J. Stahl Bad Sex on Speed 59: Things could go sideways right about then. or they could stay okay.
2023		J. Jackson Pineapple Street 294: ‘You have a husband and a house, Sasha. Even if everything went sideways, you’d still be okay’ .