whim - hir, mušica, namisao, ideja, kaprica
Izvor: R. Filipović "Englesko hrvatski ili srpski rečnik" 1987.

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whim
/(h)wim/Noun
1.A sudden desire or change of mind, esp. one that is unusual or unexplained.
2.A windlass for raising ore or water from a mine.

Synonyms
caprice - fancy - vagary - whimsy - quirk - fad

i

http://www.merriam-webster.com/dictionary/whim

http://www.thefreedictionary.com/whim


"Penguin English Student's Dictionary":

whim - sudden wish to do something, often something not sensible or reasonable


Prevod bi mogao biti: We all have our whims.

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Note added at 48 mins (2013-01-09 14:05:18 GMT)
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Ukoliko ćemo "bube" shvatiti kao hirove, mušice, onda je "whims", a ako su "fiks ideje", onda bi odgovaralo nešto drugo.

http://idioms.thefreedictionary.com/have a screw loose

have a screw loose and have a loose screw; have got a screw loose
Inf. Fig. to be silly or eccentric. He's sort of strange. I think he's got a loose screw. Yes, he has a screw loose somewhere. He wears a heavy jacket in the middle of summer.

Serbian term (edited): Svi imamo svoje bube u glavi

Every man had his own quirks and twists" (Harriet Beecher Stowe).

quirk (kwûrk)
n.
1. A peculiarity of behavior; an idiosyncrasy: "Every man had his own quirks and twists" (Harriet Beecher Stowe).
2. An unpredictable or unaccountable act or event; a vagary: a quirk of fate.
...
[Origin unknown.]
quirki·ly adv.
quirki·ness n.
quirky adj.
quirk [kwɜːk]
n
1. an individual peculiarity of character; mannerism or foible
...
[of unknown origin]

ThesaurusLegend: Synonyms
Noun 1. quirk - a strange attitude or habit
queerness, quirkiness, oddity, crotchet
strangeness, unfamiliarity - unusualness as a consequence of not being well known
[http://www.thefreedictionary.com/quirk]

Evo još mogućnosti (pored već predložene - "a bee in one's bonnet"), ref. Srpsko-engleski rečnik idioma, B. Milosavljević, M. Vilijams-Milosavljević
Buba u glavi - fiksna ideja <-> a cranky obsession
- a bee in one's bonnet
- a pet idea
- a hobby horse
- a mania
- a maggot in one's brain/head