spastic adj.

late 14c., "sudden violent muscular contraction," from Old French spasme (13c.) and directly from Latin spasmus "a spasm," from Greek spasmos "a spasm, convulsion; wincing; violent movement," from span "draw (a sword, etc.), pull out, pluck; tear away, drag; suck in; slurp down; contract violently," which is perhaps from a PIE *(s)peh- "to draw, set in motion (violently)," hence "to stretch." The figurative sense of "a sudden convulsion" (of emotion, politics, etc.) is attested by 1817.

also spazz, by 1959, U.S. teen slang phrase, typically in later use a put-down, apparently a derogatory shortening of spastic (n.). Also used as a verb, by 1972, often with out (adv.). Related: Spazzed; spazzing.

My Daddy is a regular spaz. You don't know what a spaz is? Let me tell you. A spaz is a guy who's completely out of this world—but I mean, completely. [Parade Magazine, March 1, 1959]

[Y]our teen-aged daughter asks what you think of her "shades," which you are canny enough to know are her sunglasses, and you say, "cool," and she says, "oh dad, what a spaz!" [Russell Baker column, April 13, 1965]