Idiot:
Someone who says stupid things and puts stuff in the wrong place. But he/she then apologizes and sometimes continues to do more stuff.
Troll:
Posts something extrememly obviously not fitting (like requests in the add-ons section) and never replies, leaving posters to rant and rave while the troll watches them for fun.
SOMEONE should be banning those people more often and deleting those topics. The trolls are just getting their way.