I’m afraid this question might turn out to be stupid, but I’ll give it a try. I’d like to know if it’s a set phrase and its meaning.
”My mother didn’t have a heart, Kreacher,” Sirius snapped. “She kept herself alive out of pure spite.”
Kreacher bowed again and said, “Whatever Master says,” then muttered furiously, “Master is not fit to wipe slime from his mother’s boots, oh my poor Mistress, what would she say if she saw Kreacher serving him, how she hated him, what a disappointment he was – “ (Harry Potter 5 [US Version]: p.109)[Bold font is mine]
N.B.: Kreacher hates Sirius, his Master. He respects his late Mistress, Sirius’s mother.
I’m wondering if it might be related to wipe one’s boots on (to treat with indignity), but I have no idea. Kreacher is a little crazy, indeed, but I still can’t understand why Kreacher brought up slime and boots here. Slime might have figurative meaning of dishonorable things, but why boots?
Would you give me the right meaning and tell me if it’s a set phrase?