autobautizarse

To call or dub oneself something, usually a name, title, or label one adopts without anyone else conferring it: la banda se autobautizó "Los Rebeldes". Journalistic and informal; almost always about a chosen nickname or label.

• El grupo se autobautizó 'Los Rebeldes' antes de su primer concierto. — The band dubbed itself 'Los Rebeldes' before its first concert.
• Se autobautizó como el 'rey de la salsa' en sus redes sociales. — He dubbed himself the 'king of salsa' on his social media.
• El movimiento se autobautizó con un nombre provisional. — The movement gave itself a provisional name.

Using autobautizarse for the religious sacrament of baptism — it never refers to that; it's exclusively the figurative sense of self-naming or self-labeling.