僭稱

僭称
jiànchēng
to give sb or sth a title one has no authority to give

CEDICT

to make an improper claim; to profess inappropriately

Wiktionary

超越本分，冒用稱號。

重編國語辭典

Entry Composition

1 僭 jiàn (bound form) to overstep one's authority
2 稱 chēng
  1. to weigh
  2. to state
  3. to name
  4. name
  5. appellation
  6. to praise