Was guckst du?

gucken (sometimes kucken in Plattdeutsch) is a mainly slang word meaning 'to look'. (It exists as 'keek' in most dialects of Scots).

"Was guckst du?" as a phrase means approximately "What are you looking for?" (it is a moderately aggressive way of saying this).

There was a famous TV programme called this a few years back.
Source(s):
http://www.imdb.com/title/tt0279612/

http://ingeb.org/Lieder/wennderz.html