How to make it so that you don't end up seeing some of your more childish, uninformed, embarrassing, possibly incriminating posts re-appearing decades from now in some Usenet archive at the worst possible moment:

You'll have to figure out how to alter headers in your favorite mail/news reading program (if you're using a dedicated newsreader, you may just have to find the configuration option to turn it on.) Google will also respect x-no-archive if it's the first line of a post, but that's non-standard.

I use pine for both mail and news, so I just put it into the customized-hdrs line of configuation.

customized-hdrs = From:
                                                      Reply-to:
                                                      X-No-Archive: yes

From and reply-to were included because in an old version of pine, if you specified any "custom" headers you needed to specify certain other headers if you wanted to see them when you turned on full headers. I don't know if that's the case in newer versions . . . the configuration setup is six years old at this point! ;)