'Avoir la braguette ouverte': The French can be uncreative with the classic 'your zipper is undone' warning.
When you analyse how Europeans help male friends out of potentially embarrassing situations, there's no shortage of potent connections (or red faces). Characteristically, the French can't resist showing their Republicanism, with 'the city hall is open' (La mairie est ouverte).
Away from nationalist tendencies, you are also likely to hear 'the shop is open', (le magasin est ouvert). The Catalans find that signifying a zipper as a store where your wares are kept is not specific enough: 'the pharmacy is open' (tenir la farmàcia oberta).
The Poles keep it general by referring to the gesture of zipping: 'zip up under your neck' (zapnij si pod szyj).
But you can rely on the Germans to bring in the animal connection, with cheeky remarks like 'your stable is open' (dein Hosenstall ist offen). The Italians and Spaniards take this animal connection to feathery levels; 'your bird is escaping' (respectively: scappa l'uccellino/ se escapa tu pajarillo/ pajarito). Despite the 'flighty' and saucy 'warm-blooded body' suggestions, the virile hint of 'man as provider' can still be contrived: birds build nests and lay eggs.
Meanwhile, the 'fly' in English is another name for zipper. The Brits choose to make polite comments on the appropriateness of the situation: 'you're flying without a license'. They would have you dismiss all phallic connotations with an undone zipper, instead hinting at the need for 'legal' permission to let your member fly free.