Does anyone know what a bonnacker is? Frank McCourt used the word either in Angela's Ashes or 'Tis but I cannot find out what it really means. It is a disparaging Irish slang term but that's all I know. About 40 years ago, my grandmother uttered the word and my mother got all upset as if Grandma had said some terrible swear word in front of me.

huh. that doesn't really fit with this link

Apparently there is a place in Germany too called Bonnacker.
Link
Could it have been a family thing. A 'disparaging' word only counting within the family?

Considering tsuwm's Wiki link it might be that it was considered a disparaging term in Ms. Lindstrom's family because they didn't want to be associated with "working class".