autodesignarse

To claim a title, role, or authority without being formally elected or appointed by anyone else — used critically, much like autodenominarse, especially in politics and organizational disputes.

• Se autodesignó portavoz del grupo sin que nadie lo votara. — He appointed himself spokesman for the group without anyone voting for him.
• El general se autodesignó presidente tras el golpe de estado. — The general appointed himself president after the coup.
• No puedes autodesignarte juez de lo que está bien o mal. — You can't appoint yourself judge of what's right or wrong.

Learners sometimes miss the negative connotation — it almost always implies the self-appointment lacks legitimate authority behind it.

Often confused with nombrar.