1
general::
Become extremely upset or angry, as in Dad will go ballistic when he sees you dented the new car. This expression, a variation on GO BESERK, originally alluded to a guided missile going out of control. [Slang; mid-1980s]
American Heritage Idioms
2
general::
Phrase(s): go ballistic [and] go postal
Fig. to become irrationally enraged. (Ballistic refers to a missile launching; postal refers to an enraged post office employee attacking those at his place of work. See also go into orbit.) • The boss went ballistic when he saw my expense report. • She was so mad, I thought she was going to go postal.
McGrawhill's American Idioms And Phrasal Verbs