Disc 2 of the Region 1 DVD has several easter eggs, including at least three "commercials" for Menchi-based foodstuffs. Every menu on the disk has one or more "folder" icons. Various combinations of arrow keys will light them up; trial and error will find them very quickly. Almost all of them show some kind of short clip.
If you have time to wiggle those nasty things, why don't you chew peanuts with your eyes and eat spaghetti through your nose, you affront to God!
Every episode of the North American DVD release has different joke credits (at least three or four items per episode) during the listing of the ADV Films staff. For example, episode one lists "Ms. Calvello's Wardrobe by Straightjackets R Us", while episode nine includes "Who knows what evil lurks in the nostrils of men? The Shadow nose".