1
general::
Stop paying attention, dissociate oneself from a situation, as in When Felicia starts talking about her ailments and her friends' ailments, I totally zone out. This idiom Also occurs in the passive as bezonedout and originally alluded to narcotic intoxication and then was broadened to other kinds of dissociation. For a near synonym, see TUNE OUT, def. 2. [Slang; second half of 1900s]
American Heritage Idioms