Green’s Dictionary of Slang

1. (Aus.) cheekiness [= lip n.¹ (1a)].

2002

Pete’s Aussie Sl. Home Page 🌐 slippery dip: lip, cheekiness.

2. (Aus. prison) LSD [= trip n.⁴ (1b)].

1990

Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Lucky dip. Lysergic acid. [...] Also ‘slippery dip’.