Literal translation
he has a fine forelock
Meaning
he has some nerve
Explanation
The expression signals, with disapproval tinged with astonishment, that someone shows remarkable nerve or impertinence. Literally, a un brave toupet translates as he has a fine forelock: brave here does not carry its ordinary sense of brave or courageous, but works as a familiar intensifier meaning considerable, quite a, much like the adverb bravamen (much, considerably) attested elsewhere in our sources; toupet, which originally names the tuft of hair standing up on the forehead, came by extension to symbolize the brazenness of someone who acts without embarrassment. The register is familiar, used to denounce, with a touch of reluctant admiration, the cheek of someone who dares to ask, say, or do something out of place. The expression matches exactly the French avoir un sacré toupet or avoir du culot, sharing the same hair based metaphor for brazen boldness.