Meaning: Turning into a greedy, self-righteous, murderous psychopath. Turning on your best friend and trying to kill him, killing a little girl with little to no thought, putting an end to your own mama's life after she's given birth to your sibling.
That kid, Carl, man. He went Full Shane and dropped his mama; he's gunna need some serious mental help when he grows up.
That bitch be crazy. She threw knives at me, smashed my XBOX, and completely destroyed my place; after going Full Shane on me, she calls the next morning for a booty call.
Fogey/fogy /fougi/ sl. (early 18C+, orig. Scot) old-fashioned, stuck-in-the mud.
Person with old fashioned ideas which he is unwilling to change: Come to the disco and stop being such an old fogey!
You think me an old fogeyand an old tory, his thoughtful voice said. I saw three generations since O’Connel’s time. I remember the famine. Do you know that the orange lodges agitated for repeal of the union twenty years before O’Connel did or before the prelates of your communion denounced him as a demagogue? You fenians forget some things. (James Joyce, Ulysses. Penguin Books,1992. p. 38)