Whats the post credit ending??

It's pretty much as described in the Crazy credits section: "After the end credits is a scene of Dr. Russell going crazy in his padded cell". Basically, Dr. Russell is just staring at the camera and humming "Singing in the Rain" (an obvious reference to McDowell's role in A Clockwork Orange) and then he kisses the camera and laughs maniacally. The end.