It's considered poor form to delete a post or comment on LW, since it makes it impossible to tell what the replies were talking about. (Also, it doesn't restore the karma.)

What's preferable, if one regrets a comment, is to edit it in a manner that keeps it clear what the original comment was, or to add a disclaimer. Here's one example— note that if cousin_it had just deleted the post, it would be more difficult to understand the comments on it.

Or a fake example:

Oh yeah, well your MOM coherently extrapolated my volition last night

should probably be edited to

Oh yeah, well (inappropriate joke, sorry)

if the content is to be removed.