TWACK v. To strike with great force using the back of the middle finger (usually the nail) after coiling it under pressure against the opposing thumb. Accomplished twackers can inflict great welts upon their victim's flesh.\n> That turd cutter pissed me off, so I twacked him right in the munt!\n> On the first twack\n> Pope jumped like a macaque;\n> On the second twack\n> Pope was taken aback;\n> On the third twack\n> Lost his marbles the old hack.\n> (A. S. Pushkin)\n