'Monkey bollock' (colló de mico) approaches perfection and matches the English 'bee's knees', 'cat's whiskers/pyjamas' or, closer still, 'the dog's bollocks'. But dog's bollocks wouldn't go down at all well in polite English society whereas no-one in Catalonia would bat an eyelid at monkey bollock. When I first heard the expression I almost choked as it was being used to refer to some odd-looking sea-food I was in the act of swallowing. If you don't like monkeys, there's a gentler, more sensuous expression, which is teta de monja, meaning 'nun's tit'.
But returning to monkey genitals and to illustrate their versatility, the simple addition of the indirect article -'A monkey's bollock'-, can also be used to indicate either impressive size or scale, as in val un colló de mico (it's bloody expensive) or nothing at all, as in m'importa un colló de mico (I don't give a tinker's cuss). With the further addition of 'and' -'And a monkey's bollock'-, it can also act as a powerful negation tinged with disbelief, disagreement or downright disparagement, as in: 'Viva España'; 'i un colló de mico' (bullshit/rubbish/bollocks).
Sadly, none of the online machine translation services accessible from the Catalan Government's web site seem to be able to recreate this range of meaning. For example, Apertium suggests 'Neck?*co', Opentrad can do no better than 'colló Of monkey' and Google translate comes up with 'Collin monkey'. But then Google also manages to turn a pat (on the back, for example) into a 'cofart'. How? Well (it's worth the digression), copet is the diminutive of cop, a blow -in other words, a pat. But Catalan pet means fart, hence the confusion: co-pet = 'co-fart'. To the hardened translator, though, monkey bollock and a pat on the back are all part of a day's work. Never trust machine translations.