If you look at every post, they have two buttons 'Reply' and 'Quote' in the top right hand corner. Your own posts also have the 'Edit' button. But for a short period of time after you have posted there is also a 'Delete' button. This also appears in the edit screen if you are editing a post for mong fingers shortly after posting it. After the period of time (And I think it's about 15 minutes) the forum software removes this delete button.
Which means that anything really mong that you have posted and left on for any length of time can only be edited, but double and triple posts can be deleted altogether in the short period. You can still clear the text from the double posts of course.
Your last option is to bribe a mod who should be able to remove anything, even without the delete button facility. And since this is the NAAFI Bar, you'll have to go down the pet shop for hamsters to get MDN to do it for you. And I wouldn't get involved with MDN as it's better to keep your head down and hope he doesn't notice you.
Or you could just buy him a couple of Russian amputees.