avoir une crotte sur le cœur

to still feel bitter about a past hurt

The image is of something small and foul stuck right next to your heart, standing in for a grudge you can't quite shake off.

Elle a encore une crotte sur le cœur depuis leur chicane l'été dernier.

She's still holding a grudge from their falling-out last summer.

Origin uncertain. The image of something small and unpleasant lodged right by the heart makes the point on its own.

Quebec