When something is bananas or bonkers, it's a mix of the two words. I was in the garden one day when I looked at one of the trees that i had recently pruned, in a matter of weeks it had doubled in size to my disbelief. I would usually say that this was 'bananas' or 'bonkers' but I got the two mixed up and out came 'banonkers' !!!!
Look at that flying pig....that's banonkers!!!