Now today's slang expression may offend. In fact, I guarantee saying this to a Japanese person will offend them. Why would I write about something like that? Well I believe in full-disclosure. As some English-speaking people choose not to use expletives but still understand them when heard, so too, I feel, it's important to understand things you might hear in Japanese even if you would not use such words yourself.
智恵遅 (chieoku) literally means "retarded," as in someone with a mental handicap. Japanese people (young people) use this word in much the same way that American school kids use it to tease others.
You can say "智恵遅のか?" (chieoku no ka?) if you want to say "are you retarded?" in a very demeaning way. I don't recommend it - but should you find yourself around a particularly rambuncious lot of 18-year-old boys on the sports pitch, you might hear something like this. In such a case, I think it's important you understand what is being said.
A larger point comes out with this post. Japanese people are fond of using contractions. Just like English-speakers don't like to say "don't you want to" when "doncha wanna" will suffice, Japanese people don't like to say things in the "book-standard" way.
I feel this point borders on "no duh" as a little sister of mine would say.
However - let me point out that the textbook phrase here is 智恵が遅い (chie ga osoi) which literally translates as "wisdom is slow" from which we get "retarded" or the more politically correct "mentally handicapped."
So use it or don't use it as you see fit. Just another lesson you won't find in 99% of Japanese language books, classes, lessons, etc.