Spastic

In medicine, spastic refers to an alteration in muscle tone affected by the medical condition spasticity, which is seen in spastic diplegia and many other forms of cerebral palsy and also in terms such as "spastic colon". The word is derived via Latin from the Greek "spastikos" ("drawing in", "tugging" or "shaking uncontrollably").
Colloquially, "spastic" can be pejorative; though severity of this differs between the United States and the United Kingdom. Disabled people in the United Kingdom often consider "spastic" to be one of the most offensive terms related to disability.
UK and Ireland.
The medical term "spastic" came into use to describe cerebral palsy. The Scottish Council for the Care of Spastics was founded in 1946, and the Spastics Society, an English charity for people with cerebral palsy, was founded in 1951. However, the word began to be used as an insult and became a term of abuse used to imply stupidity or physical ineptness: One who is uncoordinated or incompetent, or a fool. It was often colloquially abbreviated to shorter forms such as ‘spaz’.
Although the word has a much longer history, its derogatory use grew considerably in the 1980s and this is sometimes attributed to the BBC children's TV show "Blue Peter"; during the International Year of Disabled Persons (1981), several episodes of "Blue Peter" featured a man named Joey Deacon with cerebral palsy, who was described as a "spastic". Phrases such as "joey", "deacon", and "spaz" became widely used insults amongst children at that time.
In 1994, the same year that Conservative MP Terry Dicks referred to himself in a House of Commons debate as "a spastic with cerebral palsy", the Spastics Society changed its name to Scope. The word "spastic" has been largely erased from popular English usage and is deemed unacceptable to use outside of specific medical contexts, thus reducing stigmatisation of the condition. However, UK schoolchildren allegedly developed a derogatory adaptation of the Spastic Society's new name, "scoper".
The current understanding of the word is well-illustrated by a BBC survey in 2003, which found that "spastic" was the second most offensive term in the UK relating to anyone with a disability (retard was deemed most offensive in the US and other countries). In 2007, Lynne Murphy, a linguist at the University of Sussex, described the term as being "one of the most taboo insults to a British ear".
The video game "Mario Party 8" features a scene of the board "Shy Guy Perplex Express" where the character Kamek will cast a spell to switch train cars, being "Magikoopa magic! Turn the train spastic! Make this ticket tragic!" Because of this, "Mario Party 8" was recalled in the UK but was later rereleased replacing, "spastic" with "erratic."
United States.
In American slang, the term ‘spaz’ has evolved from a derogatory description of people with disabilities, and is generally understood as a casual word for clumsiness, otherness, sometimes associated with overexcitability, excessive startle response ("jumpiness"), excessive energy, involuntary or random movement, or hyperactivity. Some of these associations use the symptoms of cerebral palsy and other related disabilities as insults.
Its usage has been documented as far back as the mid-1950s.
In 1965, film critic Pauline Kael, hypothesised that, "The term that American teenagers now use as the opposite of 'tough' is 'spaz'."
Benjamin Zimmer, editor for American dictionaries at Oxford University Press, and researcher at the University of Pennsylvania's Institute for Research in Cognitive Sciences, writes that by the mid-1960s the American usage of the term ‘spaz’ shifted from "its original sense of 'spastic or physically uncoordinated person' to something more like 'nerdy, weird, or uncool person'." 
In a June 2005 newsletter for "American Dialect Society", Zimmer reports that the "earliest [written] occurrence of uncoordinated ‘spaz’ he could find" is found in "The Elastik Band"’s 1967 "undeniably tasteless, garage-rock single" – "Spazz".
Later in 1978, Steve Martin introduced a character Charles Knerlman, a.k.a. "Chaz the Spaz" on "Saturday Night Live", in a skit with Bill Murray called "Nerds". Bill Murray later starred in the movie "Meatballs" which had a character named "Spaz". Both shows portrayed a "spaz" as a nerd, or somebody uncool in a comic setting, reinforcing the more casual use of the term in the United States by using it in a popular comedy.
The term still occasionally appears in North American movies or TV series such as "Friends" as a mildly pejorative word. As such it receives a different reaction from British and American audiences. In one episode, Rachel refers to herself as a "laundry spaz" due to her inability to competently do the laundry which directly relates to the original meaning about physical ability. This comment was deemed offensive enough by the British Board of Film Classification to give the episode a 12 rating. Other episodes in the series are rated a step lower at PG. Similarly, Rugrats: "Tales from the Crib" Snow White got a PG rating based on Angelica calling Kimi "Spazzy".
The difference in appreciation of the term between British and American audiences was highlighted by an incident with the golfer Tiger Woods; after losing the US Masters Tournament in 2006, he said, "I was so in control from tee to green, the best I've played for years ... But as soon as I got on the green I was a spaz." His remarks were broadcast and drew no attention in America. But they were widely reported in the United Kingdom, where they caused offence and were condemned by a representative of Scope and Tanni Grey-Thompson, a prominent paralympian. On learning of the furore over his comments, Woods' representative promptly apologized.
Shortly after Weird Al Yankovic's song "Word Crimes" was released, Yankovic stated that he had been unaware that the word "spastic" used in the song is "considered a highly offensive slur by some people", particularly in the United Kingdom, and apologized for its presence in his lyrics.
Australia.
In Australian English, for some time, terms such as "spastic" and "crippled" were considered the proper words to describe persons with various disabilities and even appeared on traffic signs warning drivers of such persons near the road. More recently, these terms have fallen out of use and replaced with the more socially acceptable and generic "disabled".
Products including the term "spaz".
Multiple products in America use the word 'spaz' as part of their name.
Controversy arises if products are sold in the UK under the same name. In particular the manufacturers and importers of the "Spazz" wheelchair were criticised by the British charity Scope when they put the wheelchair on sale in the UK. Scope expressed a fear that the usage of the word as an insult would increase again, after a steady decline since the 1980s.
A caffeinated lip balm created by a police officer is called "SpazzStick." "Spaz-Stix" is a company that produces high end remote control car / plane paints.
The Transformers Power Core Combiners line of robot toys was to include a character named "Spastic". Hasbro, the makers of Transformers, said that it would not release "Spastic" in the UK. This did not stop vocal British fans from alerting various news outlets, eventually resulting in the name being changed for all markets to the less-offensive "Over-Run". The online biography for another Transformer, Strafe, originally described him as "spastic", but was changed to "twitchy" when the controversy erupted.
On 29 June 2007, Ubisoft of France pulled one of their games called "", for referring to players who did not perform well at the game as "Super Spastic". The company stated "As soon as we were made aware of the issue we stopped distribution of the product and are now working with retailers to pull the game off the market." One of the playable characters in the Jazz Jackrabbit series of games, a brother of the eponymous main character, is named "Spaz" (introduced in Jazz Jackrabbit 2). Similarly, Nintendo recalled "Mario Party 8" in the UK after releasing a version containing the line "turn the train spastic" in its dialogue.