My favorite lines
From Buckaroo Banzai Across the 8th Dimension
"Laugh a-while-a you can, Monkey-boy!"
“President's calling, Buckaroo.” “President of what?"
The corporal wants to now if the alien situation is resolved or if they should just go ahead and blow up Russia?
Buckaroo says
"Yes on one. No on two."
Buckaroo finds out Professor Hikita has been shanghaied (kidnapped) and he responds
"Aw, the deuce you say..." Perfect deadpan delivery. who else could be Buckaroo but Peter Weller?
Emilio Lizardo:
Shut up, John Big-Booty, you coward... you the weakest (veakest) individual I ever know!
One of the aliens John Parker arrives at the Buckaroo/Hong Kong Cavaliers compound, & he walks up to the gate in his pink jacket, some drug addled guy off camera says
"Nice jacket, man..."
And of course all the more serious lines quoted by other posters.