an abbreviation of 'Sean's Tiny Dick'
a pathetic human being, who sends pornographic images of his microscopic penis to females and assumes they get sexually aroused by it, when really, there is nothing there to sexually excite them...
Female: "OMG! EEWWW! WTF! THIS FREAK SENT ME A NAKED PICTURE OF HIMSELF!"
Female's Boyfriend: "WTF? IM GONNA KILL HIM!!"
Boyfriend's Friend: "There's no need to kill him, because there is nothing to be jealous about... he hasn't got anything there to be able to do anything to your girl ;)"