I am not sure what the hidden geek joke was, but the main one was that all of these characters are popular villians. Left to right, they are: The Red Skull, Darth Vader, Frankenstein's Monster, Shredder, and Cobra Commander. I will not waste space by saying what franchise they are from. There is also some foot belonging to someone off panel. The artwork was great in this one and it reminded me of something from Mad magazine. I love how all the characters have those pointed shoes.
I myself was never good at drawing shoes and they always came out pointed. The only shoes I could ever draw well were cowboy boots. I really like the detail put into everything, particularly with the shadings. While a humorous submission, it always pays to have good artwork. Darth Vader looks like he's, uh, black.