A Derwen is a colloquial term for a person who is or acts stupid or retarded. It refers to a large estate (The Derwen) where people with learning disabilities live,run a garden shop and have a college. It is a term which comes traditionally from Oswestry, North Shropshire but is begining to recieve more mainstream usage.
"Dont be such a derwen"
*someone falls over* "Haha! Derwen!"
*Someone gets something incorrect "Your a Derwen. "
Mainly Used to Degrade people.