Meaning of freak flag in English:

freak flag

noun

informal North American usually in phrase let one's freak flag fly
  • Used in reference to the open, proud, or defiant exhibition of traits regarded as unconventional.

    • ‘you should embrace your weirdness and let your freak flag fly’
    • ‘get your freak flags out!’

Origin

1960s from freak + flag; earliest use found in the Jimi Hendrix song If 6 was 9 (1967).