1
general::
1. Record one's time of departure from work, as in We never punch out at exactly five o'clock. This usage, dating from the 1920s, alludes to the use of a time clock. Also see PUNCH IN, def. 1. 2. Eject from a military aircraft, as in The pilot punched out just before the plane blew up. [Slang; 1960s]
American Heritage Idioms
2
general::
Phrase(s): punch someone out
Sl. to overcome or beat someone by punching. • He threatened to punch me out. • The thug punched out the cop and ran down an alley., Phrase(s): punch out
to record that one has left one’s workplace at a certain time. • Why didn’t you punch out when you left last night? • I punched out at the regular time.
McGrawhill's American Idioms And Phrasal Verbs