1
general::
Phrase(s): least of all
the thing of smallest importance. (Compare this with most of all.) • There were many things wrong with the new house. Least of all, the water faucets leaked. • What a bad day. Many things went wrong, but least of all, I tore my shirt.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Especially not. For example, No one cared, least of all the manager, or None of them will attend, least of all Jim. [Late 1800s]
American Heritage Idioms