Insult used by Irish dairy farmers in the mid-eighteenth century to imply that someone was like butter (aka slippery, as in untrustworthy). Kind of a catchall insult similar to « fuck you! »
Ye took my cow, ye slippery brick!
I canna believe ye slept with Connor’s wife, ye really slipped his brick.
Approaching someone from behind, grabbing & pulling your cock up so the balls elevate with it, then straddling & dragging your dank ballsack across someone's shoulder.
Richard pissed me off, so I gave him a slippery brick