Literal translation
he's a big ill-graced one
Meaning
he's a grumpy, unhelpful sort
Explanation
Someone grumpy, always in a bad mood, unhelpful, whether man or woman. In Provençal, gros works as an intensifier (equivalent to very) with no reference to size, and the pejorative prefix mau turns gracious (pleasant) into its opposite. In Provence, where courtesy calls for a smile and helpfulness toward others even when one isn't feeling well oneself, such behavior goes down badly, hence the need for the expression.