A person who visits the "urban Dictionary" website with the intention of reading peoples entries, and then giving them a thumbs down. Often these people have had traumatic events in their lives that have caused them to be so full of hate and anger that the only way they can express their hate on the world is to give people "thumbs down" on a website meant for peoples amusement and pleasure.
Jonnie: Hey man, I'm feeling angry because my Momma made me eat cold beans when I was little, and I need a way to let the world know I'm suffering and angry, what should I do?
Stevie: Why don't you go on the urban dictionary website and become a "Thumb Downer"? Just read something that someone has wrote for your amusement, then give it a thumbs down. I do it all the time!
Jonnie: Thats great advice, Thanks Stevie, People like you make the world a great place to be!
Pathetic life form that systematically goes through Urban Dictionary´s "Word of the Day" list giving a thumbs down to every single definition without reading any of them. Out of spite and utter lack of creativity, finds more exciting to downgrade the work of others than to come up with even a run of the mill (conventional, mediocre, prevalent, regular, trite) idea.
Get a life Thumbdowner, life is short and then we die.