A B767-300 DURING PREFLT AND COCKPIT SETUP THE CAPT; FO AND RELIEF PLT WERE VERBALLY ASSAULTED BY THE MAINT LEAD TECHNICIAN WHEN REQUESTED TO CLEAN THE COCKPIT WINDOWS.

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ACFT ARRIVED XA21Z IN ZZZ FROM ORD. SCHEDULED DEP WAS XB40Z; FLT XYZ. UPON ARR IN COCKPIT; FO WITNESSED A VERBAL ALTERCATION BTWN THE CAPT AND THE MAINT CREW CHIEF STEMMING FROM THE CAPT'S EARLIER REQUEST TO CLEAN THE WINDOWS. CREW CHIEF WAS VISIBLY UPSET -- ANIMATED; VERY LOUD -- AND THE ALTERCATION INTERFERED WITH BOTH THE ORIGINATION PREFLT AND THE FO'S NAV SETUP. THE ADDITIONAL STRESS; CONFUSION; AND DISTR WERE IDENTED BY THE CAPT WHO THEN DISMISSED THE CREW CHIEF FROM THE FLT DECK. THE CREW CHIEF CONTINUED HIS VERBAL ASSAULT FROM THE COCKPIT DOORWAY; TELLING THE CAPT HE WAS 'NO GOOD' AND YELLED INTO THE COCKPIT 'DON'T COME BACK.' ALL 3 COCKPIT CREW MEMBERS FELT ASSAULTED. THE CREW CHIEF'S BEHAVIOR THREATENED FLC SAFETY AT A MOST CRITICAL TIME -- DIRECTLY INCREASED THE DEP DELAY; CAUSED ADDITIONAL CONFUSION AND DISTR FOR THE FLC; AND CLRLY INCREASED THE STRESS LEVEL ON THE FLT DECK AS WE PREPARED THE ACFT FOR DEP. I HAVE NEVER WITNESSED SUCH OPEN DISGUST TOWARD ANOTHER EMPLOYEE GROUP IN MY 14 YRS WITH ACR AND I WAS SHOCKED. THE CAPT CALLED FOR THE CREW CHIEF'S SUPVR; WHO CAME TO THE FLT DECK AND APOLOGIZED FOR HIS EMPLOYEE. UNBELIEVABLY; THERE IS MORE. THE MAINT CREW CHIEF THEN RETURNED TO THE FLT DECK WITH DEP IMMINENT; PLACED ADDITIONAL WRITING IN THE LOGBOOK BEHIND THE CAPT'S BACK WITHOUT CONSULTATION; AND THEN QUICKLY DEPARTED. I WAS UNDER THE IMPRESSION THAT WE WERE BEING WORKED ON THE GND BY A NEW CREW CHIEF FOLLOWING THE ALTERCATION AND SUPVR APOLOGY; SO I WAS TAKEN ABACK TO SEE THE FELLOW IN THE COCKPIT AGAIN. THIS CAUSED ADDITIONAL DISCUSSION AND DELAY CONCERNING WHAT HAD BEEN PLACED IN THE LOGBOOK WITHOUT THE CAPT'S KNOWLEDGE WHILE TWR WAS AUTHORIZING PUSH AND THE FINAL CHKLIST WAS BEING VERBALIZED.