The practice itself has no known origin and invlolves the insertion of items (commonly a finger) into a male's anus whilst fellatio is being perfomed to enable the "smedee" to reach climax when it may not naturally happen.
The term Smedding was first coined by the erotic novelist Donatien Alphonse François de Sade (the Marquis De Sade) in his first novel Justine (Les Infortunes de la Vertu), first published in 1791.
The main character Justine is seen to be performing fellatio on another main character Mikael Smedkovic who asks the young maiden to insert an un-named root vegetable (commonly believed to be a carrot) into his anus to enable him to climax after consuming a large amount of Absinthe.
I was having a pissed up wank last night and fell asleep as it was taking so long, I wish I had 'Smed' myself.
It only takes me a few minutes to cum while I am 'Smedding' myself.