The Creepypasta Wiki defines creepypasta as "essentially internet horror stories, passed around on forums and other sites to disturb and frighten readers." This Wiki is devoted to what happens when those horror stories backfire completely.
Bad creepypasta, also known as retarded creepypasta, or crappypasta, is, of course, when a creepypasta stops being scary and just begins to enter the realms of stupid. It could be because of cliché overuse, writing the whole thing in caps, being straight up pretentious, not working out its own easily explainable mystery, having numerous spelling and grammar mistakes ... anything.
Troll pasta is deliberately bad creepypasta, made to spoof the clichés of the genre. The three most famous troll pastas are:
THEN WHO WAS PHONE - spoofs unimaginative stories and bad grammar
THEN A SKELETON POPPED OUT - spoofs anticlimaxes and stories written in caps only
TEH DAY OF ALL TEH BLOD - spoofs just about everything