The unfortunate habit of n00bs, idiots, and morons to perpetually use the caps lock key, even when "yelling" is not implied. This is usually accompanied by other obvious examples of ineptitude, such as poor grammar, spelling, and total lack of punctuation or use of paragraphs.
They seem to lack absolutely any capacity to use a keyboard, and clearly struggle to achieve even the most basic of communication tasks, thus rendering them "handicapslocked".
"HI BRIAN I JUST WANTED TO LET YOU KNOW IM GOING TO THE BAR TONIGHT R U?" -Nicky, the handicapslocked.