Literal translation
he always has a fart running on him
Meaning
he's always got some small nagging worry
Explanation
This expression describes someone forever afflicted with a small nuisance, minor but plainly tiresome for those around them, whether in terms of health or mood. Pet (fart, but also firecracker) is used figuratively for a minor annoyance, a recurring irritation ; li courre (runs on him, from courre, to run, but also to roam) plays on the verb's double meaning, suggesting both that trouble is brewing, the way a rumour is said to run, and the more physical, comic idea of a fart spreading. This double reading, at once abstract and bodily, gives the expression its bite : the person's trouble is presented as almost organic, a nature that constantly produces small nuisances. The register is very familiar, used in affectionate derision about someone who complains often without it ever being serious, the profile of a chronic grumbler whom those around are more amused by than worried for.