This scene is from the end of the episode in the fourth season entitled "AKA Superman" - episode #16.
Lois has been trying to have a birthday party for Clark and it keeps not happening (also they haven't seen much of each other - famous line "Do you realize it's been over a week since we made love" -- "Eight days, four hours, six minutes, and two seconds. But who's counting"
So at the end of the ep they are alone at last and can't hardly make it in their door without tearing each other's clothes off. But little did they know the office had set up a surprise birthday party for Clark.
Hee hee.
Better now?