1 - Pull up outside the local boulangerie/patisserie/boucherie in as large and British a four-wheel drive car as possible - a Range Rover is ideal - with the windows down so that the extremely loud English language radio service can have the full effect.
2 - Casually park your car blocking as much pedestrian access and light from the small shop as possible.
3 - On entering the shop, point at various items and sneer, saying things like, "These are far better in Sainsbury's" and "I don't know why they can't do proper bread/cakes/meat" as loudly as you can.
4 - When it's your turn to be served and the shopkeeper says politely, "Bonjour Monsieur/Madame" don't reply with any form of pleasantry but simply ask (loudly, and in English) for, "A baguette/apple pie/pound of sausages please" and if you're feeling particularly witty you can add, "pour le breakfast/dinner/tea" and fall about laughing.
5 - If the shopkeeper doesn't understand you and politely replies, "Pardon Monsieur/Madame?" simply repeat your request word for word but louder while miming eating.
6 - After eventually being served never pay with anything less than a FF200 (£20) note.
7 - As you leave the shop say something like, "They're so bloody ignorant" or "You'd think they'd understand the lingo by now".
This works every single time.