Green’s Dictionary of Slang

mullet n.1

[abbr. mullethead n.]

(Aus./US) a fool.

[UK]Star (N.Z.) 19 May 2/3: The mater was a mullet if ever there was one. I used to tell her I was a real bad egg, but her vanity was so stupendous it would not ler believe me.
[Aus]Smith’s Wkly (Sydney) 2 Dec. 18/3: ‘I’ve been robbed,’ he roared. Up rushed another mullet with the same story.
[US]J. Blake letter 10 Oct. in Joint (1972) 70: If I don’t have bread, I may look round for a likely prospect (locally, ‘mullet’) to buy it for me. However, this entails the real danger that the mullet will want to come along with me, thus beginning the day with a spate of paralyzing conversation.
[Aus]‘Nino Culotta’ Gone Fishin’ 14: I have often been called a mullet. Sometimes I have been called a prawn-headed mullet.
[US]D. Pearce Cool Hand Luke (1967) 63: Ah got me a pair of mullets what think they can beat me out on the time.
[US]Eble Campus Sl. Nov. 4: mullet – a person who is gullible or easily persuaded.
[Aus]R.G. Barrett Real Thing 82: You two have got to be the biggest pair of Botany Bay mullets I’ve ever seen. You come in with your big gobs open every time.

In compounds

In phrases

like a stunned mullet (adj.) (also like a baffled mullet)

(Aus./N.Z.) dull, stupefied.

[Aus]Sporting Globe (Melbourne) 9 Oct. 2/6: All the week end I have been walking round like a stunned mullet wondering why I didn’t [...] have a headlong tilt at Ajax in the Melbourne Stakes.
[Aus]Baker Aus. Speaks 267: [Similes] Dullness: (looking) like a stunned mullet.
[Aus]Aus. Women’s Wkly 17 May 5/3: I sit like a stunned mullet from go to whoa.
[Aus]R. Beckett Dinkum Aussie Dict. 49: Stunned mullet: If someone has an expresssion like a stunned mullet that person is deemed to be both stupid and ugly.
[UK]Guardian Rev. 31 July 12: Guests [...] sit like baffled mullets wondering if they might get a word in.
[UK]Guardian Guide 31 July–6 Aug. 23: They might look like a couple of stunned mullets.
[NZ] McGill Reed Dict. of N.Z. Sl.
[Aus]L. Redhead Peepshow [ebook] I waited by the door like a stunned mullet.