Does any one rip their own ding dong off in this movie?

Not quite, the 'monster' does have his missing but if you follow the film's plot, it's presumed that his Mother rips it off. Although he does rip off his own thumb during the early part of the film, to get his hand out of a manacle.

If you want to check out some ding-dong removal action, I suggest you watch Cannibal Ferox, Cannibal Holocaust and I Spit on your Grave. :)

He's never shown on screen ripping off his ding dong. This scene must be in a work print somewhere because I'm sure it must exist.

Maybe on the upcoming blu-ray release we'll get "Castle Freak: The Final Cut" which will include the aforementioned ding dong ripping off scene, and maybe some clarity on whether or not the castle freak is a replicant.

On a somewhat related note you might be interested in "The Invisible Maniac" where the titular invisible maniac kills a guy with a submarine sandwich.

No ding-dong-ripping, but the titular freak does kill a housecat.

No. I always believed that his mother cut it off as part of her sick and twisted punishment of this poor child (because of what his father had done to her).