Anonymously mail a tube of "Fart Stoppers" corks to your prank victim. This is not discrete at all. It will be super embarrassing to whoever receives this. Hopefully it's in front of a lot of people.
Who do you want to embarrass by having this "Butthole Stretcher" mailer sent to them? There's nothing actually in the box, except for a card saying that they have been pranked. By that time, it's already too late because of the not-so-discrete packaging meant to get attention. Your mail carrier, friends, and family ...