Normally, something like this wouldn't pass for a post all it's own, but seeing as how the Bears have decided to hibernate and do absolutely nothing, it gets more press time.
Pro Football Reference has done a post on the Worst QBs of All Time. If you break the list down based on worst seasons our own Kyle Orton makes an appearance, though one could find many other reasons for that season aside from Orton's performance.
He appears as the 16th worst season behind such notables as Ryan Leaf, Kerry Collins, Jake Plummer and Vinny Testaverde.
Looking at the worst performances by year Orton's 2005 campaign came out on top, based on an adjusted yards per pass attempt (some formula factoring in interceptions and sacks) where his yards per throw number was 2.97.
Again, that year he came in as a rookie as a starter after Rex Grossman blew out an ankle or a knee or whatever it was that year and Chad Hutchinson surprised nobody by turning out to be a turd, so Orton had no training camp time with the first team and had to learn as he went.