'Oh My Heavenly Days'
An expression of shock/disbelief/horror/surprise/happiness.
Often used by the character Bree Van de Kamp in Desperate Housewives. Variant of OMG.
'OMHD, there are giant mutant ants trying to crawl through my window! What should I do?'
'OMHD, my dad embarassed me so much today. I thought I was gonna die.'