Not kosher. Plain and simple. Doesn't mean anything else. This can mean literally not kosher, as in not adhering to Jewish dietary laws, or not kosher in the more metaphorical sense, as in not legitimate. The latter usage definitely falls into the category of slang.
Sometimes spelled 'treyf'. It's a transliteration from Yiddish.
Literal: Pork fried rice is treif.
Metaphorical: Mike's urine test was treif. He use'd Bill's piss because he was tokin' last Tuesday and didn't want it to show up.
Word Verification. Some sites (like Blogger) have an option for the moderator to require comment posters to type in a random set of letters in order to make a comment. This requirement weeds out some comment spambots. Occasionally the Word Verification letters are eerily or humorously related to the content of the comment, and the poster will reference this in the comment with "WV: word. Example sentence."
Alternate spelling (or maybe the guys at TSG just don't know how to spell) for the word conk. It refers to a means of straightening frizzy hair, or the resulting hairstyle subsequent to such straightening.
We found this one in the FBI file of Jack Lord, the late star of Hawaii Five-0 and the only white guy to wear a konk. -- From The Smoking Gun Archive.