amargar

To make bitter — literally, of taste, or figuratively, of someone's mood, experience, or life: el café se amargó, aquello le amargó la existencia. The figurative sense (to sour or ruin someone's happiness) is at least as common as the literal one.

• El café se amargó porque lo dejé hervir demasiado. — The coffee turned bitter because I let it boil too long.
• No dejes que un mal día te amargue la semana entera. — Don't let one bad day ruin your whole week.
• Su comentario le amargó la fiesta de cumpleaños. — His comment spoiled her birthday party.

Using amargarse only for taste — the figurative sense, souring someone's mood or an entire situation, is extremely common and just as central to the verb's everyday use.

Often confused with endulzar.

• expression "Amargar la vida a alguien" — A well-established Spanish idiom meaning "to make someone's life a misery," used both transitively (amargarle la vida a alguien) and reflexively (amargarse la vida).