The phrase "caught with your hand in the cookie jar" is used to condemn an action because you are supposed to use your penis for that
@geekysteven It's what Londo Mollari would do.
(Coincidentally, this is my second Centauri genitalia joke in a couple of days.)
See 30:12 here:
https://www.dailymotion.com/video/x8h3ypa
Two scenes later, Londo is caught.
