Green’s Dictionary of Slang

1. (US) a lie, a trick, a hoax; thus give the magoo v., to deceive someone.

[1912		Ade Knocking the Neighbors 140: He was putting his Nixey Mark on that Green Magoo].
1952		W.R. Burnett Little Men, Big World 25: I don’t go for that magoo.
1965		R.L. Pike Mute Witness (1997) 74: I don’t think she was giving me the magoo at that point.

2. (US) constr. with the, sex appeal.

1935		A.J. Pollock Und. Speaks.
1942		Berrey & Van den Bark Amer. Thes. Sl. §341: Sex appeal [...] (the old) magoo.

3. (US) an important person.

1933

Hecht & Fowler [title] The Great Magoo.

4. (US) a foolish person.

1933

Hecht & Fowler Great Magoo 98: If I ever lay my hands on that frizzy little magoo, I’ll maim her for life.

5. (US campus) a driver, usu. old and male, who drives very slowly and thus impedes the faster car behind.

1989

P. Munro Sl. U.