Can you target your own permanent with a spell that says 'target opponent's permanent'?

When a spell or ability uses the phrase 'target opponent's permanent,' the word 'opponent's' is a targeting restriction built into the spell's text. You may only choose a legal target, and a permanent you control is not controlled by an opponent, so it cannot be chosen as a target for that spell. This is governed by CR 114.1, which states that a target must match all criteria specified by the spell or ability.

The word 'opponent' is defined in CR 102.4 as any player who is not your teammate (or, in a non-team game, any player other than you). Since you are never your own opponent, a permanent you control will never satisfy the condition 'opponent's permanent.'

This also cannot be worked around simply by passing control of yourself — player identity is fixed. However, note that if a card's controller changes (e.g., you gain control of an opponent's permanent), that permanent is now yours and would likewise fail to meet the 'opponent's permanent' requirement.

Concrete example: Suppose a spell reads 'Destroy target opponent's creature.' You control a Grizzly Bears and your opponent controls a Serra Angel. You must target the Serra Angel — you cannot legally target your own Grizzly Bears with that spell.