I must have missed that episode.
Leonard's mom and Sheldon getting it on would be so totally wicked. Can you imagine Leonard's face? Plus Christine Baranski is the BOMB.
Following the Law of TBBT Goodness*, if they hooked up and then had a scientific discussion of it and then Leonard walked in on them, that would be the greatest scene of the entire show.
*Nerdy stuff+screentime for Sheldon+Leonard being mortified=good