1
general::
Also, not dream of. Not occur to one, not consider, as in Even if it were lying open on my desk, I wouldn't dream of reading another person's letter. This expression uses dream of in the sense of "remotely think of." [First half of 1500s]
American Heritage Idioms
2
general::
Phrase(s): wouldn’t dream of doing something
would not even consider doing something. • I wouldn’t dream of taking your money! • I’m sure that John wouldn’t dream of complaining to the manager.
McGrawhill's American Idioms And Phrasal Verbs