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1.
The freakish condition where a sadly obsessed and arguably mentally ill person continually clicks the thumb ratings of accurate Urban Dictionary words they don't like, that most people will never see anyway.
The thumb ratings of Rhondate, ERICTION, Slunthore, Enigman and Cuntrol are clearly indicating a very severe case of Urban Thumb requiring some serious therapy and/or a brutal bitch slaping.
by Jeff D September 04, 2005
 
2.
Urbanthumb is when go on urban dictionary to see if the words you have added are getting thumbs up or thumbs down. Every person who has added a word on this site has urbanthumbed.
Ill be lik 2 secs mate gotta do a urbanthumb before i come out
by D To The N December 30, 2006