A song that I often hear at this time of year (sometimes sung to this tune) contains the lyrics:
משנכנס הדר מרבין בשמחה
When Hadar walks in, we increase joy.
(This seems to be based on a variant text of the gemara in Ta'anit 29a.)
So, what is it about Hadar, King of Edom and husband of Mehetabel, that makes us so happy when he walks in?