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1.
Crazy or crazy in the head. Derived from half French half Vietnamese. Boocoo (Beaucoup) Dien cai dau (Crazy, or literally "crazy head").

A phrase used by Vietnamese street vendors to American GI's to suggest that GI's bargaining offer is crazy. Before Americans stepped onto Vietnamese soil the French were there for around 150 years so their influence can be seen.
1) GI: I will give you 10 cents for that pack of 555 Cigarettes.

Street vendor: "boocoo dinky dau or beaucoup dien cai dau", see-ga-ret phip-tin xu (cigarettes, fifteen cents/piasters).

2) Michael J. Fox: I told them, and they don't care!

Sean Penn: You dinky dau, man, you're "boocoo dinky dau or beaucoup dien cai dau"!! (You're crazy man, you're very crazy in the head!!)

No reference to chicken as suggested by some online interpretation. Although the Sino-Vietnamese word for the Chinese zodiac rooster is Dau there are two kinds of Ds in the Vietnamese language 1) a hard D as in the word Dick, Don, dog; and a soft D prounounce as a Y in the beginning of a word as in Young, yearn, year. The zodiac rooster is with the soft D as in "Yau" not the same as the hard D as in Dau, head.

Sources/Cultural reference:

1) Vietnam Voices: An Oral History of Eleven Vietnam Veterans By James F. Behr

2) Movie: Casualty of War, uttered by Sean Penn

3) HBO SHOW True Blood: PTSD suffering Vietnam Vet Terry wears a T-Shirt with "Warning: : Beaucoup Dien Cai Dau: I suffer from occasional loss of mental stability and become very violent with only slight provocation. The Veterans Administration has determined that both mental and physical harassment of my person may be hazardous to your health and well being. So stay the hell out of my face. Thank you"
by ArtieBoy@SanHo November 09, 2010