If you are really promising yourself not to swear/curse; the word Bumsniffer comes out of your mouth.

Also, if you have noticed sniffing bums really isn't pleasent. So People will also take it in as a hurtful response. Just like fuckyou, or bitchplease. IT's all the same. Bumsniffe is just the nicest form to put it in :)

You can also say it randomly. Try it, It's fun.