Alex: "Mais où est la plage, s'il vous plaît?"
CRS: "Sous les pavés, connard!"
"Where is the beach, please?" "Under the paving-stones, asshole!"
(Allusion to May '68 slogan, "Sous les pavés, la plage": "Under the paving-stones, the beach", allusion in its turn to the expanses of sand found beneath the paving-stones prised up to be used as missiles, er, paperweights).
(I'd like to draw this scene, but I'm not Cabu).