Origins of the term "funny onion"

Solution 1:

I've never heard this phrase myself in the UK, but suggest it may be a lighthearted derivative of 'Funny 'un' with ''un' being a north of England colloquialism for 'one' and 'funny 'un' rhyming with 'onion. Googling "funny 'un" brings up a bunch of references to the 'face like a Spanish/pickled onion' song.

My xxxx's is a funny'un
He's got a nose like a pickled onion
He's got a face like a squashed tomato
And eyes like green peas/We'll have some for tea/.

or

Old xxxx's a funny un
With a face like a Spanish onion
And the hairs on her *dikidido
Hang down to her knees.

or

Old xxxx's a funny un
He's (or She's) got a face like a Spanish Onion
A nose like a squashed tomato
And legs like two props/chops

So I suggest that these provide evidence that people enjoy the association of 'Funny 'un' with 'onion' and that a similar process leads to the repetitive syllable version of 'funny onion'.

*I'm choosing to assume that this means 'chin'.

Solution 2:

I grew up (in the UK) with the term 'funny onion' as a gentle description of someone being a little eccentric, but I haven't heard it in a long time. I had the feeling that 'onion' was used as a synonym for 'head' so I searched for that and found this reference in a Google ebook Wings for Our Courage: Gender, Erudition and Reuplican Thought (the reference is about half way down the page). This shows that the Florentines used 'onion' to mean 'head' although mainly in relation to decapitation.

I'm not suggesting that the British term is derived from the Florentine one but I am suggesting that a parallelism of thought could easily have lead to a similar analogy. This is particularly true since other vegetables and fruit are used as slang terms for the head: nut, coconut, swede and melon are all used, or have been used, with varying levels of insulting association.